Sensors with improved properties

ABSTRACT

A sensor or a sensor array connected to an electrical measuring apparatus is disclosed. In one embodiment, at least one sensor contains a layer of conductive modified particles which forms an electrical pathway or electrical circuit between two electrodes which are connected to an electrical measuring apparatus. In another embodiment, the first sensor contains at least one region of a nonconducting material and also a region that contains one or more modified particles. The modified particles are preferably conductive. An electrical path exists though the regions of the nonconducting material and the region containing the modified particles. The modified particles are conductive and more preferably are pigment particles such as modified carbon black, wherein the modified particles have attached at least one organic group. Alternatively, or in addition, the modified particle can be an aggregate having a carbon phase and a silicon-containing species phase and/or a metal-containing species phase wherein the aggregate optionally has attached at least one organic group. A sensor array for detecting an analyte in a fluid is also disclosed wherein each sensor emits a different response signature to an analyte wherein at least one of the sensors contains at least the modified particles as described above. Also, the present invention relates to a method for detecting the presence of an analyte in a fluid. The method involves contacting one or more sensors as described above with the analyte to generate a response and detecting the response with a detector that is operatively associated with each sensor in order to detect the presence of an analyte. Other advantages and embodiments are further described.

This application claims the benefit under 35 U.S.C. § 119(e) of priorU.S. Provisional Patent Application No. 60/173,964 filed Dec. 30, 1999,which is incorporated in its entirety by reference herein.

BACKGROUND OF THE INVENTION

In general, the present invention relates to sensors for detectinganalytes and electronic nose sensing systems and, in particular, relatesto sensors and systems using carbonaceous materials and other particles.

An electronic nose or artificial olfactory system is a device that iscapable of detecting a wide variety of analytes in vapors, gases, andliquids. The device contains an array of sensors that in the presence ofan analyte produces a response, such as an electrical response. Thedevice produces a unique signature output for a particular analyte.Using pattern recognition algorithms, the output signature can becorrelated and compared to a particular analyte or mixture of substancesthat are known. By comparing the unknown signature with the stored orknown signatures the analyte can be identified.

Current commercially available sensors can be used for a variety ofapplications. These commercial applications include, but are not limitedto, environmental toxicology and remediation, biomedicine, such asmicroorganism classification or detection, material quality control,food and agricultural products monitoring, heavy industrialmanufacturing, ambient air monitoring, worker protection, emissionscontrol, and product quality testing.

U.S. Pat. No. 5,571,401, which issued to Lewis et al., and isincorporated herein by reference in its entirety, describes sensorscomprising conducting materials and nonconducting materials arranged ina matrix of conducting and nonconducting regions. The nonconductivematerial can be a nonconducting polymer such as polystyrene. Theconductive material can be a conducting polymer, carbon black, aninorganic conductor and the like. The sensor arrays comprise at leasttwo sensors, typically about 32 sensors and in certain instances 1000 ormore sensors. The sensor arrays are useful for the detection ofanalytes. In certain embodiments, at least one of these sensorscomprises a resistor having a plurality of alternating nonconductiveregions and conductive regions and as explained therein, gaps existbetween the conductive regions and the nonconductive regions. In thesesensors, the electrical path length and resistance of a given gap arenot constant, but change as the nonconductive region absorbs, adsorbs,or imbibes an analyte. The dynamic aggregate resistance provided bythese gaps is, in part, a function of analyte permeation of thenonconductive regions.

The foregoing sensor is based on a conductive network in a nonconductivematrix. The swelling of the nonconductive matrix causes the conductiveregion to move apart, changing the resistance of the sensor. The changein the resistance of the sensor can be correlated to the concentrationof the vapor to be detected. The greater the resistance change for agiven level of vapor, the lower the detection limit of the vapor beingidentified. It is thus advantageous to maximize the resistance changeassociated with the sensor elements.

For instance, there would be a significant benefit in making sensorswhich lead to a change in resistance which is greater than conventionalsensors. There is a desire, therefore, to improve on one or morecomponents of the conventional sensors in order to achieve this greatersensitivity desired in sensors.

SUMMARY OF THE INVENTION

A feature of the present invention is to provide sensors for detectingan analyte in a fluid which are more sensitive to a variety of differentanalytes than conventional sensors.

Another feature of the present invention is to provide sensors fordetecting an analyte in a fluid, wherein the sensor can avoid the use ofa non-conducting polymer.

A further feature of the present invention is to provide sensors fordetecting an analyte in a fluid which have a greater resistance changefor a given level of vapor emitted by an analyte.

An additional feature of the present invention is to provide sensors fordetecting an analyte in a fluid wherein the time of the sensor responseis reduced.

An additional feature of the present invention is to provide sensors fordetecting an analyte in a fluid wherein the thickness of the sensor canbe reduced.

Additional features and advantages of the present invention will be setforth in part in the description that follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the description and appendedclaims.

To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to one or more sensors fordetecting an analyte in a fluid. At least one sensor for detecting ananalyte in a fluid is electrically connected to an electrical measuringapparatus. The sensor contains a layer of conductive modified particles.In other words, an electrical pathway exists through the layercontaining the conductive modified particles. The present invention, inaddition, relates to an array of sensors where at least one of thesensors is a sensor electrically connected to an electrical measuringapparatus wherein the sensor contains a layer having conductive modifiedparticles. In this embodiment, the layer containing the conductivemodified particles preferably avoids the use of a non-conductingpolymer.

The present invention further relates to sensors containing a first anda second sensor electrically connected to an electrical measuringapparatus. The first sensor contains at least one region of anonconducting material and a region that contains one or more modifiedparticles. An electrical path exists through the regions of thenonconducting material and the region containing the modified particles.The modified particles are conductive and more preferably are pigmentparticles such as modified carbon black, wherein the carbon black hasattached at least one organic group. Alternatively, or in addition, themodified particle can be an aggregate having a carbon phase and asilica-containing species phase and/or a metal-containing species phasewherein the aggregate optionally has attached at least one organicgroup.

The present invention in addition relates to a sensor array fordetecting an analyte in a fluid which involves a series of sensors asdescribed above, wherein each sensor emits a different responsesignature to an analyte wherein at least one of the sensors contains aregion of nonconducting material and a region containing at least amodified particle as described above.

Also, the present invention relates to a method for detecting thepresence of an analyte in a fluid. The method involves contacting one ormore sensors as described above with the analyte to generate a responseand detecting the response with a detector that is operativelyassociated with each sensor in order to detect the presence of ananalyte. The method further involves comparing the response signature toa library of response signatures to determine the particular analyte inthe fluid.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this invention, illustrate embodiments of the present inventionand/or provide data obtained from embodiments of the present invention,and together with the description, serve to explain the principles ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot obtained from a principle component analysis applied tothe response of modified carbon blacks to a variety of analytes.

FIG. 2 is a loadings plot of principal component analysis results ofsensors' responses.

FIG. 3 is a graph showing the response of a sensor array to variousanalytes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to several embodiments of sensors usingone or more types of modified particles which will be further describedbelow. In the first embodiment, the present invention relates to one ormore sensors for detecting an analyte in a fluid. The sensor iselectrically connected to an electrical measuring apparatus. The sensorhas a layer which contains conductive modified particles. Thus, with thesensor containing conductive modified particles, an electrical path orpathway is formed. In other words, the layer containing the conductivemodified particles is located between first and second electrodes toform, essentially an electrical circuit which has a certain resistanceas measured by the electrical measuring apparatus. The sensor having thecertain preexisting resistance is altered upon the sensor beingsubjected to an analyte which causes the resistance to be altered due tothe presence of the analyte. These changes in resistance can becorrelated to the concentration of the analyte detected and/or can beused to create odor signatures which can then be compared withpreviously recorded and/or stored response signatures. Upon comparingthe odor signature of the analyte detected with previously recordedand/or stored response signatures, a match can be made with a library ofodor signatures previously recorded in order to determine theconcentration and/or identification of the analyte. In this embodiment,the presence of a nonconducting material as in previous sensors is notnecessary and preferably is not used. The sensor containing the layer ofconductive modified particles is sufficient for the sensor to sense theanalyte and determine its concentration and/or odor signature. Thus, thesensor in this embodiment is simpler in design and more economical tomanufacture. In addition, the sensor in this embodiment is easier toproduce from the stand point that only a dispersion of modifiedparticles needs to be applied onto a substrate, for instance, in orderto form a sensor for purposes of the present invention. The layercontaining the conductive modified particles can optionally containother conducting materials as well as nonconducting materials. Examplesof other conducting materials and/or nonconducting materials aredescribed below. In addition, the modified particles are described insignificant detail below as well. The description that follows withregard to the modified particles can be used in any of the embodimentsdescribed in the present invention.

An array of sensors can also be used in this embodiment for detecting ananalyte in the fluid. At least one of the sensors contains a layerhaving the conductive modified particles. The other sensors can also usethe same design, in other words, also contain a layer of conductivemodified particles or can use sensors having conventional designs, forinstance, like the ones described in U.S. Pat. Nos. 5,571,401 and5,788,833 which are both incorporated in their entirety by referenceherein. Typically, the amount of conductive modified particles which areused to form a layer for the sensor of the present invention is anamount sufficient to form an electrical pathway between the twoelectrodes forming a part of the sensor. For purposes of the presentinvention, an amount above this amount can also be used if desired.

As another embodiment of the present invention, the present inventionrelates to sensors containing conducting materials and nonconductingmaterials arranged in a matrix of conducting and nonconducting regions.The nonconducting materials are preferably polymeric in nature and theconducting materials preferably contain at least one or more modifiedparticles.

In more detail, the sensors of the present invention used, for instance,to detect an analyte in a fluid, contain a first sensor and a secondsensor. Both sensors are electrically connected to an electricalmeasuring apparatus. The first sensor contains a region of nonconductingmaterial and a region of conducting material. Also, an electrical pathexists through the regions of nonconducting material and the regions ofthe conducting material. These sensors have a certain preexistingresistance which is altered upon the sensor being subjected to ananalyte which causes a portion of the sensor to swell leading to achange in resistance. In a preferred embodiment, the nonconductiveregion swells due to the presence of the analyte causing the conductiveregion to move apart, changing the resistance of the sensor. Thesechanges in resistance can be correlated to the concentration of theanalyte detected and further can be used to create odor signatures whichcan then be compared with previously recorded and/or stored responsesignatures. Means to compare the response signature or odor signaturewith the library of signatures recorded and/or stored previously canthen be used to match the odor signature to determine the concentrationand/or identification of the analyte.

With respect to the nonconducting regions, these regions containnonconducting materials. For instance, the nonconducting materials canbe polymeric and include, but are not limited to, main-chain carbonpolymers, main-chain acyclic heteroatom polymers, and main-chainheterocyclic polymers. The nonconducting materials can be one polymer ora combination of two or more polymers with other optional ingredientspossible, such as plasticizers and other conventional ingredientscommonly associated with the formation of polymeric articles. Examplesof various polymers include, but are not limited to, poly(dienes);poly(alkenes); poly(acrylics); poly(methacrylics); poly(vinyl ethers);poly(vinyl thioethers); poly(vinyl alcohols); poly(vinyl ketones);poly(vinyl halides); poly(vinyl nitrites); poly(vinyl esters);poly(styrenes); poly(arylenes); poly(oxides); poly(carbonates);poly(esters); poly(anhydrides); poly(urethanes); poly(sulfonates);poly(siloxanes); poly(sulfides); poly(thioesters); poly(sulfones);poly(sulfonamides); poly(amides); poly(urens); poly(phosphazenes);poly(silanes); poly(silazanes); poly(furan tetracarboxylic aciddiimides); poly(benzoxazoles); poly(oxadiazoles);poly(benzothiazinophenothiazines); poly(benzothiazoles);poly(pyrazinoquinoxalines); poly(pyromenitimides); poly(quinoxalines);poly(benzimidazoles); poly(oxindoles); poly(oxoisoindolines);poly(dioxoisoindalines); poly(triazines); poly(pyridazines);poly(piperazines); poly(pyridines); poly(piperidines); poly(triazoles);poly(pyrazoles); poly(pyrrolidines); poly(carboranes);poly(oxabicyclononanes); poly(dibenzofurans); poly(phthalides);poly(acetals); poly(anhydrides); carbohydrates, and the like.

With respect to the conducting region, preferably, the conducting regioncontains one or more modified particles. The conducting region caninclude other conducting materials and/or nonconducting materials.Examples of other conducting materials include organic conductors suchas conducting polymers; inorganic conductors such as metal and metalalloys; and mixed inorganic/organic conductors such as tetracyanoplatinate complexes, and the like. Examples of other types of conductingmaterials are set forth in U.S. Pat. Nos. 5,571,401 and 5,788,833 bothincorporated herein in their entireties by reference.

For purposes of the present invention, the modified particles arepreferably conductive particles having at least one organic groupattached to the particles. Preferably, the particle is a conductivepigment particle. The pigment can be any wide range of colors. Theparticles can be any size such as from about 100 microns or more to lessthan one micron and preferably have a size range of from about 0.05microns to about 25 microns.

The pigment can be, but is not limited to, pigments traditionally usedin ink compositions (including inkjet ink compositions), coatingcompositions (including paint formulations), liquid and solid toners,films, plastics, rubbers, and the like. Examples include, but are notlimited to, black pigments (e.g., carbon products like carbon black) andother colored pigments (e.g., polymeric and organic pigments). Carbonblack is preferred. Various commercial grades exist having varyingparticle size and structure, pH, channel content, surface area, amountof chain-like structure, volatile content, coarsens, each producedthrough minute adjustments in different reactors. Carbon black iscommercially available from Cabot Corporation, Boston, Mass. The surfacemodified carbon blacks and other pigments can be specifically tailoredto exhibit a variety of characteristics. Various characteristicsinclude, but are not limited to, its ability to absorb ultravioletlight, polarity, conductivity, size, permeability, solubility,dispersability, crosslinkability, temperature coefficient, interactionwith other polymers, sensor hysteresis, vapor discrimination, etc. Thus,the surface of the carbon black or other particles can be modified witha variety of functional groups in order to deliver a specific sensorcharacteristic. Special performance characteristics can be obtaineddepending on the specific surface modification employed.

The pigment may be chosen from a wide range of conventional pigments.For instance, the pigment product can be any carbon product capable ofreacting with a diazonium salt to form the modified pigment product. Thecarbon may be of the crystalline or amorphous type. Examples include,but are not limited to, graphite, carbon black, vitreous carbon,activated charcoal, activated carbon, carbon fibers, and mixturesthereof. Finely divided forms of the above are preferred. It is alsopossible to utilize mixtures of different pigment products.

The colored pigment can be blue, black, brown, cyan, green, white,violet, magenta, red, yellow, as well as mixtures thereof. Suitableclasses of colored pigments include, for example, carbon black, carbonproducts, anthraquinones, phthalocyanine blues, phthalocyanine greens,diazos, monoazos, pyranthrones, perylenes, heterocyclic yellows,quinacridones, and (thio)indigoids. Representative examples ofphthalocyanine blues include copper phthalocyanine blue and derivativesthereof (Pigment Blue 15). Representative examples of quinacridonesinclude Pigment Orange 48, Pigment Orange 49, Pigment Red 122, PigmentRed 192, Pigment Red 202, Pigment Red 206, Pigment Red 207, Pigment Red209, Pigment Violet 19 and Pigment Violet 42. Representative examples ofanthraquinones include Pigment Red 43, Pigment Red 194 (Perinone Red),Pigment Red 216 (Brominated Pyanthrone Red) and Pigment Red 226(Pyranthrone Red). Representative examples of perylenes include PigmentRed 123 (Vermillion), Pigment Red 149 (Scarlet), Pigment Red 179(Maroon), Pigment Red 190 (Red), Pigment Violet 19, Pigment Red 189(Yellow Shade Red) and Pigment Red 224. Representative examples ofthioindigoids include Pigment Red 86, Pigment Red 87, Pigment Red 88,Pigment Red 181, Pigment Red 198, Pigment Violet 36, and Pigment Violet38. Representative examples of heterocyclic yellows include PigmentYellow 1, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13,Pigment Yellow 14, Pigment Yellow 17, Pigment Yellow 65, Pigment Yellow73, Pigment Yellow 74, Pigment Yellow 151, Pigment Yellow 117, PigmentYellow 128 and Pigment Yellow 138. Such pigments are commerciallyavailable in either powder or press cake form from a number of sourcesincluding, BASF Corporation, Engelhard Corporation and Sun ChemicalCorporation. Examples of other suitable colored pigments are describedin the Colour Index, 3rd edition (The Society of Dyers and Colourists,1982). The color pigment will typically have a wide range of BET surfaceareas, as measured by nitrogen adsorption.

Other examples of particles include, but are not limited to,carbonaceous materials obtained by the pyrolysis of cellulosic, fueloil, polymeric, or other precursors, carbon cloth, carbon aerogels,pyrolized ion exchange resins, pyrolized polymer resins, mesoporouscarbon microbeads, pelleted carbon powder, nanotubes, buckyballs,densified carbon black, carbon clad materials, such as carbon cladsilica, and combinations thereof or activated versions thereof. Thecarbonaceous material can also be a waste product or by-product ofcarbonaceous material obtained by pyrolysis. Commercial examples ofcarbon black include, but are not limited to, Black Pearls® 2000 carbonblack, Black Pearls® 430 carbon black, Black Pearls® 900 carbon black,and Black Pearls® 120 carbon black, all available from CabotCorporation.

Also, for purposes of the present invention, the modified particle canbe an aggregate comprising a carbon phase and a silicon-containingspecies phase and optionally having attached at least one organic group.A description of this aggregate as well as means of making thisaggregate is described in PCT Publication No. WO 96/37547 and WO98/47971 as well as U.S. Pat. Nos. 5,830,930; 5,869,550; 5,877,238;5,919,841; 5,948,835; and 5,977,213. All of these patents andpublications are hereby incorporated in their entireties herein byreference.

The modified particle for purposes of the present invention, can also bean aggregate comprising a carbon phase and metal-containing speciesphase where the metal-containing species phase can be a variety ofdifferent metals such as magnesium, calcium, titanium, vanadium, cobalt,nickel zirconium, tin, antimony, chromium, neodymium, lead, tellurium,barium, cesium, iron, molybdenum, aluminum, and zinc, and mixturesthereof, and optionally having attached at least one organic group. Theaggregate comprising the carbon phase and a metal-containing speciesphase is described in U.S. Pat. No. 6,017,980, also hereby incorporatedin its entirety herein by reference.

Also, for purposes of the present invention, the modified particle canbe at least a partially silica-coated carbon black, such as thatdescribed in U.S. Pat. No. 5,916,934 and PCT Publication No. WO96/37547, published Nov. 28, 1996, also hereby incorporated in theirentirety herein by reference. The silica-coated carbon black can alsooptionally have at least one organic group.

With respect to the particle size of the pigments, the particle sizedistribution is based on the mean volume diameter of the pigmentparticles as measured by the dynamic light scattering method. Theparticle size distribution range can be from about 10 nm to about 1micron, and preferably is from about 10 nm to about 500 nm, morepreferably is from about 20 nm to about 300 nm, and most preferably isfrom about 50 nm to about 200 nm.

As indicated above, the modified particle is preferably a pigment havingattached at least one organic group. The organic group preferablycontains at least one aromatic group, at least one C₁-C₁₀₀ alkyl group,or mixtures thereof. Preferably, the groups attached to the particlesare crosslinkable chemical groups. For instance, the modified particlescan be suspended in a solvent, deposited on a sensor substrate andsubsequently crosslinked to enhance sensor stability.

At least one aromatic group includes, but is not limited to, unsaturatedcyclic hydrocarbons containing one or more rings and may be substitutedor unsubstituted, for example with alkyl groups. Aromatic groups includearyl groups (for example, phenyl, naphthyl, anthracenyl, and the like)and heteroaryl groups (for example, imidazolyl, pyrazolyl, pyridinyl,thienyl, thiazolyl, furyl, triazinyl, indolyl, and the like). At leastone C₁-C₁₀₀ alkyl group may be branched or unbranched, substituted orunsubstituted.

The modified particles can include at least one ionic group, ionizablegroup, or both as part of the organic group. An ionizable group is onecapable of forming an ionic group in the medium of use. The ionic groupmay be an anionic group or a cationic group and the ionizable group mayform an anion or cation. Ionizable functional groups forming anions oranionic groups include, for example, acidic groups. Ionic groups includesalts of acidic groups. The organic groups, therefore, include groupsderived from organic acids. Preferably, when an organic group containsan ionizable group forming an anion, an anionic group, or a mixture,such an organic group has a) an aromatic group or a C₁-C₁₀₀ alkyl groupand b) at least one acidic group having a pK_(a) of less than 11, or atleast one salt of an acidic group having a pK_(a) of less than 11, or amixture of at least one acidic group having a pK_(a) of less than 11 andat least one salt of an acidic group having a pK_(a) of less than 11.The pK_(a) of the acidic group refers to the pK_(a) of the organic groupas a whole, not just the acidic substituent. More preferably, the pK_(a)is less than 10 and most preferably less than 9. Preferably, thearomatic group or the alkyl group of the organic group is directlyattached to the particle, e.g., pigment. The aromatic group may befurther substituted or unsubstituted, for example, with alkyl groups.More preferably, the organic group is a phenyl or a naphthyl group andthe acidic group is a sulfonic acid group, a sulfinic acid group, aphosphonic acid group, or a carboxylic acid group. Most preferably, theorganic group is a substituted or unsubstituted sulfophenyl group or asalt thereof; a substituted or unsubstituted carboxyphenyl group or saltthereof; a substituted or unsubstituted (polysulfo)phenyl group or asalt thereof; a substituted or unsubstituted sulfonaphthyl group or asalt thereof; or a substituted or unsubstituted (polysulfo)naphthylgroup or a salt thereof.

Specific organic groups having an ionizable functional group forming ananion are p-sulfophenyl, 4-hydroxy-3-sulfophenyl, and 2-sulfoethyl.Other organic groups having ionizable functional groups forming anionscan also be used.

Examples of organic groups that are anionic in nature include, but arenot limited to, —C₆H₄—COO⁻X⁺; —C₆H—SO₃ ⁻X⁺; —C₆H₄—(PO₃)⁻²2X⁺;—C₆H₂—(COO⁻X⁺)₃; —C₆H₃—(COO⁻X⁺)₂; —(CH₂)_(z)—(COO⁻X⁺);—C₆H₄—(CH₂)_(z)—(COO⁻X⁺), wherein X⁺ is any cation such as Na⁺, H⁺, K⁺,NH₄ ⁺, Li⁺, Ca²⁺, Mg²⁺ and the like and z is an integer from 1 to 18. Asrecognized by those skilled in the art, X⁺ may be formed in-situ as partof the manufacturing process or may be associated with the aromatic oralkyl group through a typical salt swap or ion-exchange process.

Amines represent examples of ionizable functional groups that formcations or cationic groups and may be attached to the same types ofgroups as discussed above for the ionizable groups which form anions.For example, amines may be protonated to form ammonium groups in acidicmedia. Preferably, an organic group having an amine substituent has apK_(b) of less than 5. Quaternary ammonium groups (—NR₃ ⁺), quaternaryphosphonium groups (—PR₃ ⁺) and sulfonium groups (—SR₂ ⁺) also representexamples of cationic groups. Preferably, the organic group contains anaromatic group such as a phenyl or a naphthyl group and a quaternaryammonium or a quaternary phosphonium or sulfonium group. Quaternizedcyclic amines, and even quaternized aromatic amines, can also be used asthe organic group. Thus, N-substituted pyridinium compounds, such asN-methyl-pyridyl, can be used in this regard.

Examples of organic groups that are cationic in nature include, but arenot limited to, —C₆H₄N(CH₃)₃ ⁺Y⁻, —C₆H₄COCH₂N(CH₃)₃ ⁺Y⁻,—C₆H₄(NC₅H₅)⁺Y⁻, —(C₅H₄N)C₂H₅ ⁺Y, —C₆H₄COCH₂(NC₅H₅)⁺Y⁻, —(C₅H₄N)CH₃ ⁺Y⁻,and —C₆H₄CH₂N(CH₃)₃ ⁺Y⁻, wherein Y⁻ is any halide or an anion such asNO₃ ⁻, OH⁻, CH₃COO⁻ and the like; or combinations thereof. As recognizedby those skilled in the art, Y⁻ may be formed in-situ as part of themanufacturing process or may be associated with the aromatic or alkylgroup through a typical salt swap or ion-exchange process.

Further examples of representative organic groups and methods ofattachment are also described in U.S. Pat. Nos. 5,554,739; 5,559,169;5,571,311; 5,575,845; 5,630,868; 5,672,198; 5,698,016; 5,837,045;5,922,118; 5,968,243; 6,042,643; 5,900,029; 5,955,232; 5,895,522;5,885,335; 5,851,280; 5,803,959; 5,713,988; 5,707,432; and 6,110,994;and International Patent Publication Nos. WO 97/47691; WO 99/23174; WO99/31175; WO 99/51690; WO 99/63007; and WO 00/22051; all herebyincorporated in their entirety by reference herein. The groups andmethods of attachments described in International Published ApplicationNos. WO 99/23174 and WO 99/63007, can also be used and are incorporatedin their entirety by reference herein.

Advantageously, the modified particles used in the present invention areeasy to disperse in a wide variety of solvents. Suitable surfacemodifications include, but are not limited to, covalent attachment,noncovalent attachment and electrostatic attachment of functional groupsor ligands to the particles. The modification of the particles caninvolve functional groups of various polarities, molecular sizes,functionality, reactive groups, and dispersibilities. Groups that can beattached include, but are not limited to, polymers, alkanes, alkenes,alkynes, dienes, alicyclic hydrocarbons, arenes, heterocyclics,alcohols, ethers, ketones, aldehydes, carbonyls, carbanions, polynucleararomatics and derivatives of such organics, functional groups, chiralgroups, polyethylene glycol, surfactants, detergents, biomolecules,polysaccharides, protein complexes, polypeptides, dendrimeric materials,oligonucleotides, fluorescent moieties and radioactive groups. Incertain instances, the sensors containing the modified particles arecovalently modified to have more than one attached group or mixturesthereof.

Additional examples of organic groups that can be attached include, butare not limited to, alkyl groups, 18-carbon alkyl groups, 4-carbon alkylgroups, alkyl esters, oligoethers, and anionic groups. Additionalmodifications include, but are not limited to,poly(chloromethylstyrene), poly(alkylacrylate), alkyl esters and anionicgroups. The foregoing ligands include isomers, diasteromers, chiralgroups, racemic modifications, and other modifications.

Chemical moieties suitable to use to modify the ligands include, but arenot limited to, alkyl, bromo, chloro, iodo, fluoro, amino, hydroxyl,thio, phosphino, alkylthio, cyano, nitro, amido, carboxyl, aryl,heterocyclyl, ferrocenyl, or heteroaryl. The ligands can be attached tothe particle, such as carbon black, by various methods including, butnot limited to, covalent attachment and electrostatic attachment.

Further examples of the ionic or ionizable groups are amphiphiliccounterions, which may be cationic or anionic in nature. An amphiphiliccounterion is a molecule or compound typically described as having ahydrophilic polar “head” and a hydrophobic “tail.” Representativeexamples of cationic and anionic amphiphilic counterions include thoseset forth and described in U.S. Pat. No. 5,698,016 to Adams et al., theentire description of which is incorporated herein by reference.

For purposes of further illustrating the present invention, anamphiphilic counterion can be used. The modified pigment, as describedherein, preferably has a cationic functionality (i.e. positive charge)or anionic functionality (negative charge). The charge preferably iscreated by the ionic or ionizable group of the aromatic group or C₁-C₁₀₀alkyl group attached to the pigment. If the organic group of themodified pigment is anionic in nature, then the amphiphilic counterionwill be cationic or positive charging. Similarly, if the organic groupof the modified pigment is cationic in nature, then the amphiphiliccounterion will be anionic or negative charging. Examples of cationicamphiphilic counterions include, but are not limited to, those describedammonium ions that may be formed from adding acids to the following: afatty amine, an ester of an amino alcohol, an alkylamine, a polymercontaining an amine functionality, a polyethoxylated amine, apolypropoxylated amine, a polyethoxylated polypropoxylated amine, ananiline and derivatives thereof, a fatty alcohol ester of amino acid, apolyamine N-alkylated with a dialkyl succinate ester, a heterocyclicamine, a guanidine derived from a fatty amine, a guanidine derived froman alkylamine, a guanidine derived from an arylamine, an amidine derivedfrom a fatty amine, an amidine derived from a fatty acid, an amidinederived from an alkylamine, or an amidine derived from an arylamine. ThepKa of the ammonium ion is preferably greater than the pKa of theprotonated form of the aromatic or alkyl group on the pigment.

Specific examples of cationic amphiphilic ions include dioctylammonium,oleylammonium, stearylammonium, dodecylammonium,dimethyldodecylammonium, stearylguanidinium, oleylguanidinium,soyalkylammonium, cocoalkylammonium, oleylammoniumethoxylate, protonateddiethanolaminedimyristate, and N-oleyldimethylammonium. Generally, toform the ammonium ions described above, the various compounds describedabove such as fatty amines, esters of amino alcohols, etc., are reactedwith an acid such as carboxylic acid, a mineral acid, an alkyl sulfonicacid, or an aryl sulfonic acid.

Quaternary ammonium salts can also be used as the sources of thecationic amphiphilic ion. Examples include, but are not limited to, afatty alkyl trimethyl ammonium, a di(fatty alkyl)dimethylammonium, analkyl trimethyl ammonium, or 1-alkyl pyridinium salt, where thecounterion is a halide, methosulfate, sulfonate, a sulfate or the like.Also, phosphonium salts, such as tetraphenylphosphonium chloride can beused as the sources of the amphiphilic ion.

Cationic amphiphilic ions for use in the present invention include thoserepresented by the formula R₄N⁺, wherein R is independently hydrogen,C₁-C₃₀ alkyl, C₁-C₃₀ alkenyl, C₇-C₃₀ aralkyl, and C₇-C₃₀ alkaryl.Another example of a suitable amphiphilic ion is a polymer containing anammonium ion derived from an amine containing polymer. The aminecontaining polymer can be a copolymer of an amine containing monomer,such as dimethylaminoethyl methacrylate or acrylate, or vinylpyridine orvinylimidazole, and another monomer such as methyl acrylate, methylmethacrylate, butyl acrylate, styrene, and the like. The polymer mayalso be a polyethyleneimine (PEI), derivatized or acylated PEI,polyallylamine, or polydiallylamine. The polymer may also be a ter- ortetra-polymer containing a mixture of an amine containing monomer andtwo or three other amine containing monomers, respectively. Such apolymer may be prepared by any means, such as radical (emulsion,suspension, or solution) or anionic polymerization, stable free radicalpolymerization or atom transfer polymerization.

As stated earlier, the amphiphilic counterion can alternatively be ananionic amphiphilic counterion. Examples of such anionic amphiphilicions include, but are not limited to, an alkylbenzene sulfonate, analkyl sulfonate, an alkylsulfate, a sulfosuccinate, a sarcosine, analcohol ethoxylate sulfate, an alcohol ethoxylate sulfonate, an alkylphosphate, an alkylethoxylated phosphate, an ethoxylated alkylphenolsulfate, a fatty carboxylate, a taurate, an isethionate, an aliphaticcarboxylate, or an ion derived from a polymer containing an acid group.Sources of specific and preferred examples of anionic amphiphilic ionsinclude, but are not limited to, sodium dodecylbenzene sulfonate, asodium dodecylsulfate, Aerosol OT, an oleic acid salt, a ricinoleic acidsalt, a myrisitic acid salt, a caproic acid salt, sodium2-octyldodecanoate, sodium bis(2-ethylhexyl)sulfosuccinate, a sulfonatedpolystyrene, or homo- or copolymers of acrylic acid or methacrylic acidor salts thereof.

Generally, the above-identified amphiphilic counterions and relatedcompounds are commercially available in salt form or can be routinelymade by one of ordinary skill in the art.

Other examples of organic groups that can be attached to the pigment orparticle include groups with the following formulas. In each of thefollowing formulas, —X is attached directly to the pigment and —X′ canbe directly attached to the pigment. Each of the following organicgroups, for purposes of the present invention, can optionally contain anionic group, an ionizable group, or both.

A further example of a modified pigment is a pigment having attached atleast one group comprising the formula:

—X-Sp-[NIon]_(p)R

wherein X represents an aromatic group or an alkyl group, NIonrepresents at least one non-ionic group, Sp represents a spacer group, Rrepresents hydrogen, an aromatic group, or an alkyl group, and p is aninteger of from 1 to 500.

The aromatic group with respect to the X substituent and/or the Rsubstituent can be substituted or unsubstituted and can be, forinstance, an aryl or heteroaryl group. The aromatic group can besubstituted with any group, such as one or more alkyl groups or arylgroups. Preferably, the aromatic group is a phenyl, naphthyl,anthracenyl, phenanthrenyl, biphenyl, pyridinyl, benzothiadiazolyl, orbenzothiazolyl. Examples of the alkyl group with respect to the Xsubstituent and/or the R substituent include, but are not limited to,substituted or unsubstituted alkyl groups which may be branched orunbranched. The alkyl group can be substituted with one or more groups,such as aromatic groups. Preferred examples of the alkyl group forpurposes of the X substituent include, but are not limited to, C₁-C₁₂,like methyl, ethyl, propyl, butyl, pentyl, or hexyl groups. In otherwords, X and/or R can represent a branched or unbranched, substituted orunsubstituted, saturated or unsaturated hydrocarbon. Examples ofsubstituted groups include, but are not limited to, an ester group, anamide group, an ether group, a carboxyl group, an aryl group, an alkylgroup, and the like.

Sp or the spacer group as used herein is a link between two groups andcan be a bond, or a chemical group such as, but not limited to, CO₂,SO₂CH₂CH₂, CH₂CH₂, CHR″CH₂, CH₂CHR″, CHR″, O₂C, SO₂, CO, SO₃, OSO₂,SO₃NR″, R″NSO₂, NHCO, CONR″, NR″CO₂, O₂CNR″, NR″CONR″, O, S, NR″,SO₂C₂H₄, arylene, alkylene, NR″CO, NHCO₂, O₂CNH, NCHONH, and the like,wherein R″, which can be the same or different, represents an organicgroup such as a substituted or unsubstituted aryl and/or alkyl group.

Examples of the non-ionic group include, but are not limited to, groupshaving no apparent ionic charge, such as polymers of ethylene oxide,propylene oxide, other alkylene oxides, carboxylic acid esters, glycols,alcohols, esters, alkanolamine-fatty acid condensates, silicones,isocyanates, alkylpyrrolidenes, and alkylpolyglycosides. In non-aqueousmedia, the non-ionic group, in addition to the aforementioned groups,may have carboxylates, sulfonates, phosphates, amines, and other groupsthat typically demonstrate an ionic nature in water. The non-ionic groupis preferably a C₁-C₁₂ alkyl group, or a C₁-C₁₂ alkylene oxide group. pcan be 1-25, 26-50, 51-75, 75-100, and/or 101-500, and p preferably is 5to 50.

The X substituent and/or non-ionic group may be substituted with one ormore functional groups. The functional group preferably contains alypophilic group. Examples of functional groups include, but are notlimited to, R′, OR′, COR′, COOR′, OCOR′, carboxylates, halogens, CN,NR′₂, SO₃H, sulfonates, —OSO₃ ⁻, NR′(COR′), CONR′₂, NO₂, PO₃H₂,phosphonates, phosphates, N═NR′, SOR′, NSO₂R′, wherein R′ which can bethe same or different, is independently hydrogen, branched or unbranchedC₁-C₂₀ substituted or unsubstituted, saturated or unsaturatedhydrocarbons, e.g., alkyl, alkenyl, alkynyl, substituted orunsubstituted aryl, substituted or unsubstituted heteroaryl, substitutedor unsubstituted alkylaryl, or substituted or unsubstituted arylalkyl.

Amines also represent examples of functional groups as well asquaternary ammonium groups (—NR₃ ⁺) and quaternary phosphonium groups(—PR₃ ⁺), as well as quaternary sulfonium groups (—SR₂ ⁺).

In an additional embodiment of the present invention, the modifiedpigment can be a pigment having attached at least one group comprisingthe formula:

—X-Sp-[A]_(p)R

wherein X represents an aromatic group or an alkyl group; Sp representsa spacer group; A represents an alkylene oxide group of from about 1 toabout 12 carbons; p represents an integer of from 1 to 500, and Rrepresents hydrogen, a substituted or unsubstituted alkyl group, or asubstituted or unsubstituted aromatic group. A can be the same ordifferent when p is greater than 1. X can be substituted orunsubstituted and can include substituted groups such as an ester group,an amide group, an ether group, a carbonyl group, an aryl group, analkyl group and the like. The substituted groups can be attached orlinked to A.

Examples of preferred alkylene groups include, but are not limited to,—CH₂—CH₂—O—; —CH(CH₃)—CH₂—O—; —CH₂CH₂CH₂—O—; —CH₂CHCH₃—O—; orcombinations thereof.

In another embodiment of the present invention, the modified pigment canbe a pigment having attached at least one group comprising the formula:

—X-Sp-[(-CH₂)_(m)—O—)_(p)—R]

wherein X is described above, and for instance can represent an aromaticgroup or an alkyl group as described earlier, m is an integer of from 1to 12, preferably 2 or 3, p is an integer of from 1 to 500, Sprepresents a spacer group, and R is described above, and for instancecan be hydrogen, a substituted or unsubstituted alkyl group, or asubstituted or unsubstituted aromatic group. Examples of R substituentsinclude, but are not limited to, hydrogen, methyl, ethyl, butyl, orpropyl groups. p can be 1-25, 26-50, 51-75, 76-100, and 101-500, and ispreferably 5 to 50. Particularly preferred groups of this formula arewhere X is a phenylene group, m is 1 to 5, and more preferably 2 or 3, pis 5 to 50, more preferably 44-45, and R is hydrogen or a methyl group.Another preferred group is where m is 2, p is 7, R is a methyl group,and X is a phenylene group.

In yet another embodiment of the present invention, the modified pigmentcan be a pigment having attached at least one polymeric group, whereinthe polymeric group comprises the formula:

—X-Sp-[polymer]R

wherein X and Sp are described above, and for instance can represent atleast an aromatic group or at least an alkyl group as described earlier,“polymer” represents a polymeric group comprising repeating monomergroups or multiple monomer groups or both, optionally having at leastone —X′ group. The group “polymer” can be substituted or unsubstitutedwith additional groups. R is described above and for instance canrepresent hydrogen, a bond, a substituted or unsubstituted alkyl group,or a substituted or unsubstituted aromatic group. X′ represents anaromatic group or alkyl group, and each X′ and X can be the same ordifferent. The total monomer repeating units that comprise the group“polymer” is not greater than about 5,000 monomer repeating units. Xand/or X′ can be substituted or unsubstituted and can includesubstituted groups such as an ester group, an amide group, an ethergroup, and the like. The substituted groups can be linked to the group“polymer.” Also, when R represents a bond, the available bond can beattached to the pigment. The polymeric group can be any polymeric groupcapable of being attached to a pigment.

For purposes of the present invention and this formula immediatelyabove, one or more polymeric groups that comprise the group “polymer”can be present. The polymeric group can be a thermoplastic polymericgroup or a thermosetting polymeric group. Further, the polymeric groupcan be a homopolymer, copolymer, terpolymer, and/or a polymer containingany number of different repeating units. Further, the polymeric grouppresent in the present invention can be any type of polymeric group,such as a random polymer, alternating polymer, graft polymer, blockpolymer, star-like polymer, and/or comb-like polymer. The polymericgroup used in the present invention can also be one or more polyblends.The polymeric group can be an interpenetrating polymer network (IPN);simultaneous interpenetrating polymer network (SIN); or interpenetratingelastomeric network (IEN).

Specific examples of polymeric groups include, but are not limited to,linear-high polymers such as polyethylene, poly(vinylchloride),polyisobutylene, polystyrene, polycaprolactam (nylon), polyisoprene, andthe like. Other general classes of polymeric groups of the presentinvention are polyamides, polycarbonates, polyelectrolytes, polyesters,polyethers, (polyhydroxy)benzenes, polyimides, polymers containingsulfur (such as polysulfides, (polyphenylene) sulfide, andpolysulfones), polyolefins, polymethylbenzenes, polystyrene and styrenecopolymers (ABS included), acetal polymers, acrylic polymers,acrylonitrile polymers and copolymers, polyolefins containing halogen(such as polyvinyl chloride and polyvinylidene chloride),fluoropolymers, ionomeric polymers, polymers containing ketone group(s),liquid crystal polymers, polyamide-imides, polymers containing olefinicdouble bond(s) (such as polybutadiene, polydicyclopentadiene),polyolefin copolymers, polyphenylene oxides, polysiloxanes, poly(vinylalcohols), polyurethanes, thermoplastic elastomers, and the like.

Generally, the polymeric groups described in Volume 18 of theEncyclopedia of Chemical Technology, KIRK-OTHMER, (1982), page 328 topage 887, and Modern Plastics Encyclopedia '98, pages B-3 to B-210, and“Polymers: Structure and Properties,” by C. A. Daniels, TechnomicPublishing Co., Lancaster, Pa. (1989), all incorporated in theirentirety herein by reference, can be used as the polymeric groups whichcomprise the group “polymer”. These polymeric groups can be prepared ina number of ways and such ways are known to those skilled in the art.The above referenced KIRK-OTHMER section, Modern Plastics Encyclopedia,and C. A. Daniels' reference provide methods in which these polymericgroups can be prepared.

The polymeric group can be preferably a polyolefin group, a polyurethanegroup, a polystyrenic group, a polyacrylate group, a polyamide group, apolyester group, or mixtures thereof. Examples of R groups can be thesame as previously described above. p can be 1-25, 26-50, 51-75, 76-100,101-500, and is preferably 1 to 100, and more preferably 5 to 50.

Also, the organic group(s) attached to the pigment can be one or moretypes of dyes, such as, but not limited to, Nile Blue A, Toluidine Blue,Tryan Blue, C.I. Acid Blue 40, C.I. Acid Blue 129, C.I. Acid Blue 9,C.I. Acid Blue 185, C.I. Direct Blue 71, C.I. Direct Blue 199, C.I.Direct Red 9, C.I. Acid Red 18, C.I. Acid Red 27, C.I. Direct Yellow 86,C.I. Direct Yellow 4, C.I. Acid Yellow 23, and C.I. Food Black 2.Besides the organic group comprising the dye, an organic group having anionic group and a counterionic group can have a dye serving as thecounterionic group. Attaching a dye to the pigment can provide theadvantage of modifying the color properties of the pigments. Also, theorganic group(s) attached to the pigment can be one or more types oflight stabilizers, e.g., hindered amine light stabilizer (HALS) orantioxidant.

In an embodiment of the present invention, the modified particle can bea polymer coated modified particle, such as a modified pigment product.For instance, the modified pigment is at least partially coated with oneor more polymers and can be substantially or fully coated by one or morepolymers. The use of the term “coated” includes partially and fullycoated carbon products and modified pigment products. The polymer inthis invention partially or fully encapsulates the modified pigmentproduct, wherein the modified pigment product is the core and thepolymer is the shell. The polymer(s) coated onto or used to encapsulatethe modified pigment product is preferably present on the modifiedpigment product such that the polymer(s) is not substantiallyextractable by a solvent. More preferably, the polymer(s) on themodified pigment product is attached by physical (e.g., adsorption)and/or chemical means (e.g. chemical bonding, grafting).

The modified pigment product coated with a polymer can be a modifiedpigment product having at least one organic group attached to thepigment product. The organic group can be substituted with an ionic,ionizable, or polar group. The pigment product which has the organicgroup attached thereto can be any pigment product capable of having atleast one organic group attached to the pigment product.

Another set of organic groups which may be attached to the pigment areorganic groups having an aminophenyl, such as (C₆H₄)—NH₂,(C₆H₄)—CH₂—(C₆H₄)—NH₂, (C₆H₄)—SO₂—(C₆H₄)—NH₂. Organic groups alsoinclude aromatic sulfides, represented, for instance, by the formulasAr—S_(n)—Ar′ or Ar—S_(n)—Ar″, wherein Ar and Ar′ are independentlyarylene groups, Ar″ is an aryl and n is 1 to 8.

Preferably, the organic group comprises an aromatic group and/or aC₁-C₁₀₀ alkyl group (and more preferably a C₁-C₁₂ alkyl group) directlyattached to the particle, such as a pigment, optionally with an ionic,ionizable, or polar group.

More than one type of organic group can be attached to the particle, ortwo or more modified particles with different attached organic groupscan be used. Using two or more different types of organic groups permitsa combination of properties. If two different types of organic groupsare attached, for example, a sulfanilic group and a styrenic group, thesulfanilic group promotes dispersibility and the styrenic group servesas a radical grafting site. The ratio of the different organic groupscan be the same or different.

A minimum treatment level of the ionic, ionizable, or polar group can beused to impart stability to the dispersion. For example, groups such asionic species (e.g., sulphates, phosphates, alkali salts of organicacids or quaternary ammonium salts), non-ionic species (e.g., hydroxyl,organic acids) or surfactant stabilizers (e.g., SDMS, SDS, Antarox) canbe used to provide stable particle dispersions in aqueous media.Dispersion of the modified particle in organic liquids can befacilitated in a similar manner but employing treatments which are morecompatible with these less polar environments. Treatment levels of theorganic group for purposes of radical grafting sites would depend onmaterial uses. For instance, attachment of epoxy groups would facilitategrafting to hydroxyl bearing polymer matrices such as polyurethanes orpolycarbonates or amine matrices such as nylon. Other examples includethe attachment of radical sensitive vinyl groups such as styrenics oracrylates, or methacrylates, to facilitate crosslinking type reactionsin radical polymerizations.

Also, a combination of different modified particles can be used. Forinstance, a modified pigment having one type of organic group attachedthereto can be used in combination with another modified pigment havinga different organic group attached thereto. Also, a modified pigmentsuch as an aggregate comprising a carbon phase and a silicon-containingspecies phase can be used in combination with a modified carbon producthaving an attached organic group, and so on.

The modified particle which is coated with one or more polymers can haveany particle size and/or surface area so long as the particle is capableof being at least partially coated with one or more polymers.Preferably, the primary particle size of the modified pigment is fromabout 5 nm to about 100 nm and more preferably from about 8 nm to about75 nm. The nitrogen surface area as measured by the BET method, of themodified carbon product is preferably from about 20 m²/g to about 1500m²/g and more preferably from about 25 m²/g to about 700 m²/g and mostpreferably from about 30 m²/g to about 250 m²/g.

The thickness of the coating on the modified particle can be uniformedor can vary in thickness. The thickness of the coating can be about 1 mmor more. Preferably, the polymer coated onto the modified particleproduct is substantially uniform in thickness. Preferably, the thicknessof the polymer coating on the modified particle is from about 10 nm toabout 100 nm, more preferably from about 20 nm to about 75 nm, and mostpreferably from about 30 nm to about 50 nm.

The modified particle can have more than one coating or shell. In otherwords, the modified particle can have multiple layers of shells orcoatings which partially or fully encapsulate the modified particle or aprevious coating or shell. The polymers comprising the various layerscan be the same or different. For instance, one layer can becross-linked while the next layer can be not cross-linked. Each of thevarious coatings, if more than one is present on the modified particle,can be substantially the same or vary in thickness if desired.

The polymer which is coated onto the modified particle can be ahomo-polymer, copolymer, terpolymer, and/or a polymer containing anynumber of different repeating units.

The polymer can be any type of polymer, such as a random polymer,alternating polymer, graft polymer, block polymer, star-like polymer,and/or comb-like polymer. The polymer can also be one or morepolyblends. The polymer can be an interpenetrating polymer network(IPN); simultaneous interpenetrating polymer network (SIN); orinterpenetrating elastomeric network (IEN). The polymer can bethermoplastic or thermosettable.

Specific examples of polymers include, but are not limited to, linearand non-linear polymers such as polyethylene, poly(vinylchloride),polyisobutylene, polystyrene, polycaprolactam (nylon), polyisoprene, andthe like. Other general classes of polymers include polyamides,polycarbonates, polyelectrolytes, polyesters, polyethers,(polyhydroxy)benzenes, polyimides, polymers containing sulfur (such aspolysulfides, (polyphenylene) sulfide, and polysulfones, polyolefins,polymethylbenzenes, polystyrene and styrene copolymers (ABS included),acetal polymers, acrylic polymers, acrylonitrile polymers andcopolymers, polyolefins containing halogen (such as polyvinyl chlorideand polyvinylidene chloride), fluoropolymers, ionomeric polymers,polymers containing ketone group(s), liquid crystal polymers,polyamide-imides, polymers containing olefinic double bond(s) (such aspolybutadiene, polydicyclopentadiene), polyolefin copolymers,polyphenylene oxides, polyurethanes, thermoplastic elastomers, siliconepolymers, alkyd, epoxy, unsaturated polyester, vinyl ester, urea-,melamine-, or phenol-formaldehyde resins, and the like. More particularexamples of polymers include acrylic polymers, methacrylic polymers, orstyrenic polymers.

The polymer coated modified particles can be made by a number of waysincluding, but are not limited to, aqueous mediated polymerizationenvironments such as emulsion polymerization or suspensionpolymerization processes as well as solvent based polymerizations. Thepolymerizations involved are generally chain growth polymerizationsand/or step growth polymerizations.

In another embodiment, the modified particle, for instance a modifiedpigment, has at least one organic group attached to the pigmentparticles and the organic group is positively chargeable. The organicgroup can be attached to the pigment in various amounts, i.e., low tohigh amounts, thus allowing fine control over charge modification. Theorganic group that is attached to the pigment particles can be any groupwhich permits the modified pigment to be positively chargeable.Preferably, the organic group comprises an aromatic group or a C₁-C₂₀alkyl group, wherein either group can be substituted or unsubstituted.It is also preferred that the aromatic group or C₁-C₂₀ alkyl group isdirectly attached to the pigment particles. Preferred groups ofpositively chargeable organic groups are nitrogen containing orphosphorus containing organic groups.

Preferred positive chargeable organic groups have the generalstructures:

wherein Q represents the elements nitrogen or phosphorus; X represents acounterion such as Cl⁻, Br⁻, ArSO₃ ⁻, and the like; R₁ represents analkylene group or an arylene group attached to the pigment; and R₂, R₃,and R₄, which may be the same or different, each represent an alkylgroup or an aryl group. Preferably, the alkylene or alkyl group is aC₁-C₁₀ alkylene or alkyl group and the arylene or aryl group is a C₆-C₂₀arylene or aryl group. For the purposes of this invention, aryl andarylene groups include heteroaryl and heteroarylene groups,respectively. Other preferred organic groups that can be attached to thepigment particles include, but are not limited to the following:

in which Ar represents an aromatic group and Ar′ represents an aromaticgroup. The aromatic group includes, but is not limited to, unsaturatedcyclic hydrocarbons containing one or more rings. The aromatic group maybe substituted or unsubstituted. Aromatic groups include aryl groups(for example, phenyl, naphthyl, anthracenyl, and the like), andheteroaryl groups (imidazolyl, pyrazolyl, pyridinyl, thienyl, thiazolyl,furyl, triazinyl, indolyl, and the like). In a similar manner,negatively chargeable particles can be produced using the appropriatefunctional groups, such as sulfamides.

A combination of organic groups such as an organic group comprising apyridyl group and an organic group comprising a quaternary ammoniumgroup can be used.

As stated, the organic group is a C₁-C₁₀₀ alkyl group (more preferably aC₁-C₁₂ alkyl group), an aromatic group, or other organic group,monomeric group, or polymeric group, each optionally having a functionalgroup or ionic or ionizable group. More preferably, these groups aredirectly attached to the particles.

The polymeric group can be any polymeric group capable of being attachedto a particle. The polymeric group can be a polyolefin group, apolystyrenic group, a polyacrylate group, a polyamide group, a polyestergroup, or mixtures thereof. Monomeric groups are monomeric versions ofthe polymeric groups.

The organic group can also be an olefin group, a styrenic group, anacrylate group, an amide group, an ester, or mixtures thereof. Theorganic group can also be an aromatic group or an alkyl group, eithergroup with an olefin group, a styrenic group, an acrylate group, anamide group, an ester group, or mixtures thereof, wherein preferably thearomatic group, or the alkyl group, like a C₁-C₁₂ group, is directlyattached to the particle.

The polymeric group can include an aromatic group or an alkyl group,like a C₁-C₁₂ group, either group with a polyolefin group, apolystyrenic group, a polyacrylate group, a polyamide group, a polyestergroup, or mixtures thereof.

The organic group can also comprise an aralkyl group or alkylaryl group,which is preferably directly attached to the particle. Other examples oforganic groups include a C₁-C₁₀₀ alkyl group, such as a C₂₀-C₆₀ alkylgroup.

Examples of other organic groups are organic groups having the followingformulas (hyphens on one or more ends represents an attachment to aparticle or to another group):

—Ar—CO₂(C_(m)H_(2m+1)), where m=0 to about 20;

—Ar—(C_(n)H_(2n+1)), where n=1 to about 50;

—Ar—C_(p)H_(2p)Ar—, where p=1 to about 10;

—Ar—CX₃, where X is a halogen atom;

—Ar—O—CX₃, where X is a halogen atom;

—Ar—SO₃ ⁻;

—Ar—SO₂(C_(q)H_(2q−1)), where q=about 2 to about 10;

—Ar—S₂—Ar—NH₂;

—Ar—S₂—Ar—;

—ArSO₂H;

—Ar—((C_(n)H_(2n))COOX)_(m), where n=0 to 20, m=1 to 3, and X=H,cations, or organic group; These groups can be further activated and/orreacted with such groups as carbodiimides and further reacted withNH₂-terminated functionalization groups; SOCl₂, or PCl₃, or PCl₅ to beconverted to —Ar—(C_(n)H_(2n))COCl)_(m) groups and further reacted withOH-terminated functionalization groups.

—Ar—((C_(n)H_(2n))OH)_(m), where n=0 to 20, m=1 to 3; These groups canbe further activated and/or reacted with such groups as tosyl chlorideand subsequently reacted with amino-terminated ligands;carbonyldiimidazole and subsequently reacted with amino-terminatedligands; carbonylchloride terminated ligands; and epoxy terminatedligands.

—Ar—((C_(n)H_(2n))NH₂)_(m), where n=0 to 20, m=1 to 3, and itsprotonated form: —Ar—((C_(n)H_(2n))NH₃X)_(m), where X is an ion; Thesegroups can be further activated and/or reacted with such groups ascarbodiimide activated carboxyl-terminated ligands; carbonyldiimidazoleactivated hydroxy-terminated ligands; tosyl activated hydroxy-terminatedligands; vinyl terminated ligands; alkylhalide terminated ligands; orepoxy terminated ligands.

—Ar—((C_(n)H_(2n))CHNH₃ ⁺COO⁻)_(m) where n=0 to 20 and m=1 to 3; Thesegroups can be derivatized further by reaction through the carboxylicgroup by reaction with NH₂ or OH terminated groups or through the aminogroup by reaction with activated carboxy-terminated ligands, activatedhydroxy-terminated ligands, vinyl ligands, alkylhalide terminatedligands, or epoxy terminated ligands.

—Ar—((C_(n)H_(2n))CH═CH₂)_(m), where n=0 to 20, m=1 to 3 or—Ar—((C_(n)H_(2n))SO₂CH═CH₂)_(m), where n=0 to 20, m=1 to 3. Thesegroups can be further activated and/or reacted with such groups asamino-terminated ligands; peroxy-acids to form epoxides and subsequentlyreacted with hydroxy- or amino-terminated ligands; hydrogen halides toform —Ar((C_(n)H_(2n))CH₂CH₂X)_(m) groups and subsequently reacted withamino-terminated ligands.

Other reaction schemes can be used to form various groups onto theparticles.

Other mixtures of organic groups include the following:

—Ar—SO₃ ⁻ and —Ar(C_(n)H_(2n+1)), where n=1 to about 50;—Ar—S₂—Ar—NH₂ and —ArC_(p)H_(2p)Ar—, where p=1 to about 10;—Ar—S₂—Ar— and —ArC_(p)H_(2p)Ar—, where p=1 to about 10; orat least two different —Ar—CO₂(C_(m)H_(2m+1)), where m=0 to about 20.

The various organic, monomeric, and polymeric groups described above andbelow which are part of the modified particles can be unsubstituted orsubstituted and can be branched or linear.

As described earlier, one or more organic groups can be attached to theparticle, for example, the pigment. Further, two or more modifiedpigments, each having a different organic group attached to the pigment,can be used. Also, one organic group having an ionic or ionizable groupcan be used in connection with a second or additional organic groupswith or without ionic or ionizable groups and so on. Also, combinationsof pigments which differ, for example, by morphology or surface area,can be used. Treatment levels of the attached groups can beadvantageously varied in order to produce a variety of different sensorperformances.

As stated earlier, with respect to an embodiment of the presentinvention, the sensors of the present invention are a matrix of theconducting regions and the nonconducting regions. This matrix can beformed by dissolving the nonconducting materials into a solvent andintroducing the modified particles into the solution containing thedissolved nonconducting materials. Many techniques including, but notlimited to, solution casting, suspension casting, and mechanical mixingcan fabricate the sensors of the present invention. In general, solutioncasting routes are advantageous because they provide homogeneousstructures and are easy to process. With solution casting routes, spin,spray, or dip coating can easily fabricate resistor elements. Suspensioncasting still provides the possibility of spin, spray, or dip coating,but more heterogeneous structures than with solution casting areexpected. With mechanical mixing, there are no solubility restrictionssince it involves only the physical mixing of the resistor components,but device fabrication is more difficult since spin, spray, and dipcoating are no longer possible. In certain embodiments, the sensor orchemi-resistor is deposited as a surface layer on a solid matrix thatprovides means for supporting the leads. Typically, the solid matrix isa chemically inert, nonconductive substrate, such as a glass or ceramic.

In more detail, and as an example, in solution casting, one or more ofthe components of the chemi-resistor are suspended or dissolved in acommon solvent. A non-conductive material such as the non-conductivepolymer is dissolved in an appropriate solvent, such as THF,acetonitrile, water, and the like. The modified pigment can then besuspended into this solution and the resulting mixture is used to dipcoat electrodes. Also, mechanical mixing can be used to mix thenonconducting materials with the conducting materials such as themodified pigments. Once fabricated, the individual element forming thesensors can be optimized for a particular application by varying theirchemical makeup and morphologies. The chemical nature of thechemi-resistors determines which analytes will respond in their abilityto distinguish different analytes. The relative ratio of conducting tononconducting components determines the magnitude of the response sincethe resistance of the elements becomes more sensitive to sorbedmolecules as the percolation threshold is approached. The filmmorphology is also important in determining response characteristics.For instance, thin films respond more quickly to analytes than do thickones. Hence, with an empirical catalog of information on chemicallydiverse sensors made with varying ratios of insulating to conductingcomponents and by differing fabrication routes, sensors can be chosenthat are appropriate for the analytes expected in a particularapplication, their concentrations, and the desired response times.Further optimization can then be preformed in an iterative fashion asfeedback on the performance of an array under particular conditionsbecomes available.

With respect to the above description of the manufacturing of thesensors of the present invention for certain embodiments, the embodimentwherein the sensor contains a layer having conductive modified particlesand preferably no nonconducting material, these sensors can bemanufactured in a similar fashion. In more detail, the modifiedparticles used to form the layer for the sensor can be applied to asubstrate such as an inert substrate in the same fashion that inks areapplied to a substrate. For instance, the modified particles can beapplied by printing methods known to those skilled in the art whichinclude, but are not limited to, inkjet type printing and the like.Essentially, any means used to form a layer containing pigments or anydevice used to form an image on a substrate can be used for purposes offorming the layer of conductive modified particles for the sensor of thepresent invention. Generally, the conductive modified particles areformed into a dispersion which can be aqueous or non-aqueous and thenthis dispersion is applied to a substrate to form a layer wherein thenon-aqueous or aqueous solvent is removed, such as by evaporation orother techniques. The dispersion containing the conductive modifiedparticles can also contain other conventional ingredients typically usedin inks or coatings such as, but not limited to, binders, additives toimprove printability drying, and the like. For purposes of the presentinvention, the aqueous or non-aqueous solvent can also be considered anaqueous or non-aqueous vehicle.

The sensor arrays can comprise other different sensors, including, butnot limited to, surface acoustic wave (SAW) sensors, quartzmicrobalances, organic semiconducting gas sensors, bulk conductingpolymer sensors, polymeric coating on an optical fiber sensors,conducting/nonconducting region sensors and conducting filler ininsulating polymer sensors, dye impregnated polymeric coatings onoptical fibers, polymer composites, micro-electro-mechanical systemdevices, micromachined cantilevers, and micro-opto-electro-mechanicalsystem devices.

The chemi-resistor or sensor may itself form a substrate for attachingthe lead or the resistor or, the chemi-resistor can be deposited as asurface layer on a solid matrix which provides means for supporting theleads.

Sensor arrays particularly well-suited to scaled up production arefabricated using integrated circuit (IC) design technologies. Forexample, the resistors can easily be integrated on the front end of asimple amplifier interfaced to an A/D converter to efficiently feed thedata stream directly into a neural network software or hardware analysissection. Micro-fabrication techniques can integrate the chemiresistorsdirectly onto a micro-chip which contains the circuitry for analogsignal conditioning/processing and then data analysis. This provides forthe production of millions of incrementally different sensor elements ina single manufacturing step, for instance, using inkjet ink typetechnology. The sensor array of a million distinct elements onlyrequires a one centimeter by one centimeter sized chip employinglithography at a ten micron feature level, which is within the capacityof conventional commercial processing and deposition methods. Thistechnology permits the production of sensitive, small-size stand alonechemical sensors.

Preferred sensor arrays have a predetermined inter-sensor variation inthe structure or composition of the nonconductive regions (e.g., thenonconductive organic material). The variation may be quantitativeand/or qualitative. For example, the concentration of the nonconductiveorganic polymer in the blend can be varied across sensors.Alternatively, a variety of different organic polymers may be used indifferent sensors.

An electronic nose for detecting an analyte in a fluid is fabricated byelectrically coupling the sensor leads of an array of compositionallydifferent sensors to an electrical measuring device. The device measureschanges in resistance at each sensor of the array, preferablysimultaneously and preferably over time. Frequently, the device includesa signal processing means and is used in conjunction with a computer anddata structure for comparing a given response profile to astructure-response profile database for qualitative and quantitativeanalysis. As such, in another embodiment, the present invention relatesto a system for detecting an analyte in a fluid, comprising: a sensorarray comprising at least first and second chemically sensitiveresistors, each chemically sensitive resistor comprising a plurality ofalternating regions comprising a nonconductive region, such as anonconductive organic material, and conductive region, such as amodified carbon black conductive material, compositionally differentthan the nonconductive region. Each chemi-resistor provides anelectrical path through the alternating nonconducting region and theconductive regions, a first electrical resistance when contacted with afirst fluid comprising an analyte at a first concentration and a seconddifferent electrical resistance when contacted with a second fluidcomprising the analyte at a second different concentration, thedifference between the first electrical resistance and the secondelectrical resistance of the first chemically sensitive resistor beingdifferent from the difference between the first electrical resistanceand the second electrical resistance of the second chemically sensitiveresistor under the same conditions; an electrical measuring deviceelectrically connected to the sensor array; and a computer comprising aresident algorithm; the electrical measuring device detecting the firstand said second electrical resistances in each of said chemicallysensitive resistors and the computer assembling the resistances into asensor array response profile.

In addition, another embodiment involves a system for detecting ananalyte in a fluid, which involves a sensor array containing two or morechemically sensitive resistors or sensors. At least one of the sensorscontains a layer having conductive modified particles, as describedabove.

Typically a sensor array or electronic nose comprises at least ten,usually at least 100, and often at least 1000 different sensors, thoughwith mass deposition fabrication techniques described herein orotherwise known in the art, arrays of on the order of at least 10⁶sensors are readily produced.

In operation, each resistor provides a first electrical resistancebetween its conductive leads when the resistor is contacted with a firstfluid comprising a chemical analyte at a first concentration, and asecond electrical resistance between its conductive leads when theresistor is contacted with a second fluid comprising the same chemicalanalyte at a second different concentration. The fluids may be liquid orgaseous in nature. The first and second fluids may reflect samples fromtwo different embodiments, a change in the concentration of an analytein a fluid sampled at two time points, a sample and a negative control,etc. The sensor array necessarily comprises sensors which responddifferently to a change in an analyte concentration, i.e., thedifference between the first and second electrical resistance of onesensor is different from the difference between the first and secondelectrical resistance of another sensor. In addition, the sensor arraycan comprise redundant sensors that can be advantageous for maximizingthe signal and thus reducing the noise in the signal.

In a preferred embodiment, the temporal response of each sensor(resistance as a function of time) is recorded. The temporal response ofeach sensor may be normalized to a maximum percent increase and percentdecrease in resistance which produces a response pattern associated withthe exposure of the analyte. By iterative profiling of known analytes, astructure-function database correlating analytes and response profilesis generated. Unknown analytes may then be characterized or identifiedusing response pattern comparison and recognition algorithms.Accordingly, analyte detection systems comprising sensor arrays, anelectrical measuring device for detecting resistance across eachchemiresistor, a computer, a data structure of sensor array responseprofiles, and a comparison algorithm are provided. In anotherembodiment, the electrical measuring device is an integrated circuitcomprising neural network-based hardware and a digital-analog converter(DAC) multiplexed to each sensor, or a plurality of DACs, each connectedto different sensor(s).

In certain aspects, the present invention provides methods for the rapidconstruction of large libraries of sensors through combinatorialtechniques. Combinatorial chemistry is a generic term that describes aseries of innovative technologies that are designed to automate andsimplify the selection, synthesis, and fabrication of candidate ligandsattached to the particles(s). The initial step of the combinatorialprocess is selection of compounds such as ligands or functional groupsattached to the ligands, for inclusion in a library of compounds. Inaddition, highly automated sampling handling and analysis has beendeveloped to analyze the volume of compounds in the combinatoriallibrary.

In certain embodiments, the sensor hysteresis using the sensorscontaining the modified particles of the present invention is reduced oreliminated. The presence of hysteresis may affect the reproducibility ofthe response. As a consequence, the response is also faster with themodified sensors of the present invention. In other aspects, the sensorsof the present invention are used with other polymers to increaseselectivity. In this embodiment, the modified particles can be morereadily dispersed in certain organic solvents.

Since the goal of the array of sensors is to produce different responsesamongst two or more sensors in order to create odor signatures from thereadings obtained by the electrical measuring apparatus, there are avariety of ways to have each sensor different from each other. Thevarious variables that can be used to achieve a variety of differentsensors in order to form the array for purposes of the preferredembodiment of the present invention include, but are not limited to, a)the amount of conductive modified particle forming the layer of thesensor; b) the amount of organic group, if used, attached to theconductive particles; c) using different types of organic groups, ifused, that are attached to the conductive particles (e.g., usingpolymers of different chain lengths); d) using different conductiveparticles (e.g., using a carbon black having a different BET in onesensor compared to another sensor and yet treating both types of carbonblacks with the same organic group); e) using conventional sensors incombination with the sensors of the present invention; and f) using asensor having conductive modified particles with nonconductingmaterials. Any one or more of these variables can be used to form avariety of different sensors in order to achieve odor signatures whichcan then be used to detect the concentration of an analyte and/oridentify the analyte. Any means to alter the response of each of thesensors in the array in order to obtain a different response from sensorto sensor is preferred and can be used for purposes of the presentinvention.

The array of sensors can be formed on an integrated circuit usingsemiconductor technology methods, an example of which is disclosed inPCT Patent Application Serial No. WO 99/08105, entitled “Techniques andSystems for Analyte Detection,” published Feb. 19, 1999, and incorporateherein by reference.

A wide variety of analytes and fluids may be analyzed by the disclosedsensors, arrays and noses so long as the subject analyte is capable ofgenerating a differential response across a plurality of sensors of thearray. Analyte applications include broad ranges of chemical classesincluding, but not limited to, organics such as alkanes, alkenes,alkynes, dienes, alicyclic hydrocarbons, arenes, heterocyclics,alcohols, ethers, ketones, aldehydes, carbonyls, carbanions, polynucleararomatics and derivatives of such organics, e.g., halide derivatives,etc., microorganisms, fungi, bacteria, microbes, viruses, metabolites,biomolecules such as sugars, isoprenes and isoprenoids, fatty acids andderivatives, etc.

Accordingly, commercial applications of the sensors, arrays, and nosesinclude, but are not limited to, environmental toxicology andremediation, biomedicine, materials quality control, food andagricultural products monitoring. Further applications include, but arenot limited to: heavy industrial manufacturing (automotive, aircraft,etc.), such as ambient air monitoring, worker protection, emissionscontrol, and product quality testing; oil/gas petrochemicalapplications, such as combustible gas detection, H₂S monitoring, andhazardous leak detection and identification; emergency response and lawenforcement applications, such as illegal substance detection andidentification, arson investigation, hazardous spill identification,enclosed space surveying, and explosives detection; utility and powerapplications, such as emissions monitoring and transformer faultdetection; food/beverage/agriculture applications, such as freshnessdetection, fruit ripening control, fermentation process monitoring andcontrol, flavor composition and identification, product quality andidentification, and refrigerant and fumigant detection; cosmetic/perfumeapplications, such as fragrance formulation, product quality testing,and patent protection fingerprinting; chemical/plastics/pharmaceuticalsapplications, such as fugitive emission identification, leak detection,solvent recovery effectiveness, perimeter monitoring, and productquality testing; hazardous waste site applications, such as fugitiveemission detection and identification, leak detection andidentification, and perimeter monitoring; transportation applications,such as hazardous spill monitoring, refueling operations, shippingcontainer inspection, and diesel/gasoline/aviation fuel identification;building/residential applications, such as natural gas detection,formaldehyde detection, smoke detection, automatic ventilation control(cooking, smoking, etc.), and air intake monitoring; hospital/medicalapplications, such as anesthesia and sterilization gas detection,infectious disease detection, breath, wound and body fluids analysis,and telesurgey.

In yet another aspect, the present invention relates to a method fordetecting the presence of an analyte in a fluid, the method comprising:resistively sensing the presence of an analyte in a fluid with a sensorcomprising an array comprising at least first and second chemicallysensitive resistors each comprising a plurality of alternatingnonconductive regions, such as nonconductive organic material, andconductive-regions, such as modified particles compositionally differentthan the nonconductive region, each resistor providing an electricalpath through the nonconducting region and a region containing themodified particles, a first electrical resistance when contacted with afirst flu id comprising an analyte at a first concentration and a seconddifferent electrical resistance when contacted with a second fluidcomprising said analyte at a second different concentration.

The general method for using the disclosed sensors, arrays, andelectronic noses for detecting the presence of an analyte in a fluidinvolves resistively sensing the presence of an analyte in a fluid witha chemical sensor comprising first and second conductive leadselectrically coupled to and separated by a chemically sensitive resistoras described above by measuring a first resistance between theconductive leads when the resistor is contacted with a first fluidcomprising an analyte at a first concentration and a second differentresistance when the resistor is contacted with a second fluid comprisingthe analyte at a second different concentration.

The modified particles used in the sensors of the present applicationprovide numerous advantages over conventional sensors. For instance, thesensors containing the modified particles can be more sensitive toanalytes than conventional sensors using unmodified carbon black. Thisability to be highly sensitive to analytes can lead to greater changesin resistance, thus leading to a better discrimination value betweenvarious sensors. Furthermore, the present invention provides the abilityfor the sensor to provide faster response times upon exposure of thesensor to an analyte. In addition, the sensors of the present inventionprovide highly linear relationships to concentrations of the analyte,temperature, and humidity conditions. This can be important with respectto providing sensors that respond consistently and predictably tovariances that occur with respect to these conditions. In addition, themodified particles used in the sensors of the present application permitthe formation of various dispersions which suspend the modifiedparticles uniformly which then leads to a uniform formation of a layercontaining a uniform dispersion of the modified particle thus leading toa better response when the sensor is exposed to a variety of analytes.Also, with the modified particles used in the sensors of the presentinvention, a one step spraying process for the manufacturing of thesensors can be achieved due to the excellent suspension and dispersionof the modified particles in the solvent which eventually is sprayed toform the sensor surface of the present invention.

Also, as described above and in the examples, the ability of the sensorsusing the modified particles of the present invention do lead toexcellent discrimination power for a variety of analytes thus providingsensors which can properly and accurately detect analytes and/or theconcentration of the analytes.

The following patents and publications provide examples of components ofsensors that may be incorporated into the embodiments of the presentinvention: Zaromb, S., et al., “Theoretical basis for identification andmeasurement of air contaminants using an array of sensors having partlyoverlapping selectivities,” Sensors and Actuators, 6:225-243 (1984);Stetter, et al., “Detection of hazardous gases and vapors: Patternrecognition analysis of data from an electrochemical sensor array,”Anal. Chem., 58:860-866 (1986); Shurmer, H. V., et al., “An electronicnose: A sensitive and discriminating substitute for a mammalianolfactory system,” IEE PROCEEDINGS, 137, pt. G, No. 3:197-204 (June1990); Bartlett, P. N., et al., “Electrochemical deposition ofconducting polymers onto electronic substrates for sensor applications,”Sensors and Actuators, A21-A23:911-914 (1990); Stetter, et al., “Sensorarray and catalytic filament for chemical analysis of vapors andmixtures,” Sensors and Actuators B1, 43-47 (1990); Persaud, K. C.,“Odour detection using sensor arrays,” Analytical Proceedings,28:339-341 (10/91); Gardner, J. W., et al., “Detection of vapours andodours from a multisensor array using pattern recognition Part 1.Principal component and cluster analysis,” Sensors and Actuators B,4:109-115 (1991); Shurmer, H. V., et al., “Odour discrimination with anelectronic nose,” Sensors and Actuators G., 8:11 (1992); Grate, J. W.,et al., “Smart sensor system for trace organophosphorus and organosulfurvapor detection employing a temperature-controlled array of surfaceacoustic wave sensors, automated sample preconcentration, and patternrecognition,” Anal. Chem., 65:1868-1881 (1993); and Pearce, T. C., etal., “Electronic nose for monitoring the flavour of beers,” Analyst,118:371-377 (1993); Longergan, et al., “Array-Based Vapor Sensing UsingChemically Sensitive, Carbon Black-Polymer Resistors,” Chem. Mater.,(1996), Vol. 8, pp. 2298-2312; Severin et al., “An Investigation of theConcentration Dependence and Response to Analyte Mixtures of CarbonBlack/Insulating Organic Polymer Composite Vapor Detectors,” Anal. Chem.2000, 72, pp. 658-668; Snow et al., “Size-Induced Metal to SemiconductorTransition in a Stabilized Gold Cluster Ensemble,” Chemistry ofMaterials, Vol. 10, No. 4, (1998), pp. 947-949; Talik, et al., “SensingProperties of the CB-PCV Composites for Chlorinated HydrocarbonVapours,” Journal of Materials Science, 27 (1992) pp. 6807-6810, andU.S. Pat. Nos. 5,571,401 and 5,788,833.

The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

EXAMPLES Example 1

Modified carbon blacks were evaluated and compared to both standard andcommercially dispersed carbon blacks. The carbon blacks were modifiedwith a variety of functional groups such that a range of polarities werecovered. Several of the carbon blacks were also treated at variouslevels of modification. The standard carbon blacks used in thisexperiment were Black Pearl 2000 (BP2000), N990, Vulcan XC72, andColumbian Conductex 975. The commercially dispersed carbon blacks werethe Borden co-dispersion (Columbian Conductex 975 in toluene) andPermblak 2940 (BP2000 in water). Table I shows the various carbon blacksused as chemiresistor sensors and the solvent used to prepare thedispersion.

The sensors' performance was evaluated by exposing them to a number ofanalytes, most of them solvents. These analytes were chosen based ontheir solubility parameter to span a large “solvent space”. Isobutyricacid was also chosen as a bacteria metabolic product. The solvent spacecan be described in terms of the solubility parameter whose values forvirtually all solvents range between that of

TABLE I Description of carbon blacks used in sensor evaluation studySubstrate ID Description Solvent Standard Carbon Blacks 222 BP2000Benzene 223 N990 DMF 224 Vulcan XC72 THF 225 Columbian Conductex 975Toluene Commercially Dispersed Carbon Blacks 251 Borden Co-dispersionToluene 252 Permblak 2940 Water Surface Modified Carbon Blacks 230oligoether-modified M700 Ethanol 231 sulfanilic acid modified Elftex TPtreated with C18 cationic Dodecane amine- 232trifluormethylaniline-modified Vulcan XC-72 Ethanol (0.12 mmoles/grtreatment level) 233 trifluormethylaniline-modified Vulcan XC-72 Ethanol(0.5 mmoles/gr treatment level) 234 butylaniline-modified Vulcan 7HToluene (0.48 mmoles/gr treatment level) 235 butylaniline-modifiedVulcan 7H Toluene (0.12 mmoles/gr treatment level) 236 ethylaminobenzoate-modified Vulcan 7H Ethanol (0.48 mmoles/gr treatmentlevel) 237 ethyl aminobenzoate-modified Vulcan 7H Ethanol (0.12mmoles/gr treatment level) 238 trifluoromethylaniline-modified Vulcan 7HEthanol (0.48 mmoles/gr treatment level) 239trifluoromethylaniline-mdoified Vulcan 7H Ethanol (0.12 mmoles/grtreatment level) 240 aminophenylsulfatoethylsulfone-modified CSX-557 IPA241 Emperor S90B IPA 242 6 wt % coating of poly(chloromethylstyrene) onVulcan 7H THF 243 24 wt % coating of poly(chloromethylstyrene) on Vulcan7H THF 244 45 wt % coating of poly(chloromethylstyrene) on Vulcan 7H THF245 20 wt % poly(alkylacrylate) on Sterling 4620 THF 246 ethylaminobenzoate-modified CSX-98 THF 247 p-aminobenzoate andbis-trifluoromethylaniline-modified M700 THF 248 p-aminobenzoate andaminododecanoic acid-modified M700 Toluene 249 p-aminobenzoate andaminododecanoic acid-modified M700 Toluene 250 p-aminobenzoicacid-modified M700 Water (0.8 mmoles/gr treatment levelCarbon black dispersions could not be sprayed to a measurable baseresistance at these concentrations. isooctane (14) and water (48Mpa1/2). The solubility parameter for solvents, as described byHildebrand, can be determined from their molar energies or enthalpies ofvaporization. The Hildebrand parameter is related to the cohesive energy(i.e. the attractive strength) of the molecules. In general, the largerthe size of the molecule the higher the cohesive energy. Table II, showsthe solubility parameter for the analytes used to evaluate the sensors'response.

TABLE II Hildebrand solubility parameter, partition coefficient betweenwater and octanol, and saturated (equilibrium) vapor pressure at 25° C.for solvents used as analytes in the evaluation of carbon blackschemiresistor sensors. Solubility Saturated vapor Parameter Pressure @25° C. Solvent (MPa)^(1/2) (kPa) Dodecane 16.2 0.016 Toluene 18.2 3.79Ethyl acetate 18.6 12.60 Methyl ethyl ketone 19 12.60 Tetrahydrofuran19.5 21.60 Methylene chloride 19.8 4.77 Dimethyl sulfoxide 24.6 0.431Ethanol 26 7.87 Methanol 29.3 16.90 Water 48 2.80

All dispersions were made at a concentration of 0.75 wt % based on thetotal weight of the solvent. The solvent was chosen based on thechemical functionality of the carbon black. The carbon black was addedto the appropriate solvent and sonicated for ten minutes on speed fourat 15° C. using a Misonix XL2020 ultrasonic processor. After ten minutesthe ultrasonic processor was paused, the dispersion was removed, shakenby hand, and then replaced for an additional ten minutes. For a completelist of the carbon black and solvent combinations used please refer toTable I.

All carbon blacks were deposited using the Iwata HP-BC airbrush onto theGASS-7100A substrates. The same dispersion was sprayed on all eightsensors using circle masks with adhesive backing. The dispersions weresprayed until the measured resistance was in the kilo-ohm range or (ifthis was not possible) sprayed until the resistance level could bemeasured by the Keithley 2002 multimeter.

All substrates were post processed for one hour at room temperature atfull vacuum (<30 in. Hg) immediately following deposition and removal ofthe masks.

The sensor arrays were exposed to the eight analytes at the followingconcentrations (concentrations were calculated by dividing the saturatedvapor concentration by the dilution factor, 20):

ANALYTE CONCENTRATION (PPM) DMSO 39 Dodecane 8 Ethyl Acetate 6216Ethanol 3882 Isobutyric Acid 1993 MEK 6216 THF 10655 Toluene 1870 *Thesubstrate temperatures were maintained at 28° C. and the flow rate was400 cc/min (the sample chamber contains four sub chambers allowing forthe testing of four substrates at the same time).

The temporal response of resistance vs. time for the sensor array asthey are exposed to various vapors was analyzed using an IGOR programwhich is commercially available. Only one feature extraction of thetemporal response was done and it is termed baseline correction. Thebaseline correction method gives a fractional difference, that is,(R_(max)−R_(min))/R_(min). This technique works best for sensors thatreach equilibrium. Since no other pre-processing algorithm was used, anassumption was made that all the sensors had reached equilibrium.Principal component analysis (PCA) was applied to the response data foreight analytes from the modified carbon blacks only, and this is shownin FIG. 1 (autoscaled, and normalized −1 norm in Pirouette, a commercialsoftware by Infometrics). An outlier diagnostics was done and itindicated that 2 EA, 1 EtOH and 1 MEK where outliers and hence whereremoved from the plot.

Soft independent modeling of class analogy (SIMCA), was also done onthis data and the off-diagonal average interclass distance (ICD) was77.72 (Table IV).

TABLE IV Interclass distance after application of SIMCA DMSO DOD EA EtOHIBA MEK THF TOL DMSO 0.000 34.64 83.19 36.35 92.30 57.32 74.05 32.29 DOD34.64 0.00 48.59 75.07 95.87 42.70 41.78 32.99 EA 83.19 48.59 0.00271.26 51.07 7.79 18.04 10.06 EtOH 36.35 75.07 271.26 0.00 217.09 234.01213.73 102.22 IBA 92.30 95.87 51.07 217.09 0.00 41.69 51.97 44.19 MEK57.32 42.70 7.79 234.01 41.69 0.00 11.47 8.026 THF 74.05 41.78 18.04213.73 51.97 11.47 0.00 6.31 TOL 32.29 32.99 10.06 102.22 44.19 8.036.31 0.00 *Where DMSO is dimethyl sulfoxide; DOD is dodecan; EA is ethylacetate; EtOH is ethanol; IBA is isobutyric acid; MEK is methyl ethylketone; THF is tetrahydrofuran; TOL is toluene.

TABLE V Interclass residuals after application of SIMCA DMSO DOD EA EtOHIBA MEK THF TOL DMSO 0.617 15.09 21.22 18.17 38.01 15.25 4.084 7.63 DOD25.95 0.57 57.06 45.59 49.01 23.62 5.12 12.78 EA 35.90 22.24 0.931 31.0536.19 5.32 4.26 4.34 EtOH 16.77 25.77 19.36 0.521 30.80 10.11 6.52 10.76IBA 70.31 63.20 62.45 176.01 0.594 6.48 8.46 6.55 MEK 41.46 25.91 20.0094.01 28.86 0.506 3.586 4.48 THF 50.20 26.50 18.27 111.32 33.39 4.400.264 4.49 TOL 28.07 25.66 23.33 94.44 38.22 10.48 2.02 0.619

Good discrimination among analytes is achieved with ICD's of 6. Overlapis a likely outcome for values less than 3. As can be seen, theinterclass distances are very large for the modified carbon blacks,showing very good discrimination.

An indication of the sensors' orthogonality can be inferred from aloadings plot. A loadings plot determines which variables (sensors) areimportant for describing the variation in the original data set. Theloadings are the cosine of the angle between the principal component(PC) and the original variables. They describe how the originalmeasurement variables relate to each of the new PC axes. As the loadingsapproach 1 or −1 the angle between the PC and the variables approaches 0or 180 degrees, which means that the variable contributes much variationto the PC.² In the loadings plot where much of the variance is describedby the first three PC's sensors maximum orthogonality is observed whenthe sensors form a perfect circle. FIG. 2, shows a loadings plot of PCAresults. The loadings plot shows that even with the limitedrepresentation of chemical functionality on the modified carbon blacks,the discrimination power is still evenly distributed in athree-dimensional space. Hence, the reason for the large ICD's.

FIG. 3, shows the average (of all the exposures and for the same sensoracross a substrate) fractional difference response for the sensor arrayto eight analytes, which was obtained using the VGS. Note, that thestandard deviation is small. Tables VI-IX, show the average response forforty responses (eight sensors times five exposures each) and theresponse percent coefficient of variation (standard deviation divided byaverage, multiplied by 100) of exposure one through exposure five.Substrates 222, 246, and 247 yielded indistinguishable noisy responsesand therefore, are not included in the tables. Note that the percentcoefficient of variance is reasonably small for most of the responses.

The data shows that the commercially dispersed carbon black (substrateID 251, Borden Co-dispersion—one of the controls) yields much lowerresponse values to all analytes tested. Relative to the carbon blacksthat gave the largest responses, the difference in response forsubstrate ID 251 ranged between 9.5 times smaller for dodecane and 31.6times smaller for THF.

The data also shows that the response values for the other commerciallydispersed carbon black (substrate ID 252, Permblak 2940) and thestandard carbon blacks (substrate ID 224, Vulcan XC72 and substrate ID225, Columbian Conductex 975) ranked in the bottom four except in thecases of DMSO and ethanol where substrate ID 252 ranked tenth andtwelfth respectively. The modified carbon blacks always produced largerresponse values than the unmodified carbon blacks.

Example 2

The performance of a polymer composite sensor array (SS 605) was used tocompare to the response of the CB sensor array without the controls (ID222-225, 251 and 252, Table I)—that is, modified carbon blacks only.Table XIX, shows the average response of the array to temperature andhumidity and Table XX, shows the response time and SN ratio. Note, thatthe average performance to humidity and temperature are fairly similarfor both arrays. SS 605 performs better in terms of the response timeand SN ratio.

TABLE XIX Comparison of the performance of SS 605 to CB sensors AverageAverage Average Average Average (R − (R − (R − Average RH CC (for TC CCRo)/Ro @ Ro)/Ro @ Ro)/Ro @ sensitivity RH (PPM/C) (Temp) 25° C. 31° C.34° C. (PPM/% RH) response) SS 605 314 0.988 Toluene −308 0.923 8.68E−036.83E−03 5.96E−03 Methanol −131 0.850 3.23E−03 2.56E−03 2.02E−03 MeCl−26 0.137 1.64E−03 1.15E−03 1.16E−03 MEK −305 0.640 5.47E−03 4.11E−033.21E−03 CPS without carbon black controls 1050 0.978 Toluene −440 0.9609.93E−03 6.82E−03 6.10E−03 Methanol −403 0.927 7.22E−03 5.08E−033.53E−03 MeCl −433 0.730 1.71E−03 1.49E−03 1.35E−03 MEK −344 0.9828.68E−03 6.42E−03 5.63E−03 CPS with carbon black controls 763 0.925Toluene −335 0.934 7.51E−03 5.15E−03 4.57E−03 Methanol −276 0.8325.29E−03 3.83E−03 2.75E−03 MeCl −58 0.740 1.74E−03 1.45E−03 1.22E−03 MEK−265 0.957 6.53E−03 4.80E−03 4.18E−03 Where TC is the temperaturecoefficient and CC is the correlation coefficient.

TABLE XX Comparison of response time and signal-to-noise ratio For SS605 and CB sensors Average response % CV of time in (R − Average AverageAverage sec. @ Ro)/Ro SNR @ SNR @ SNR @ 31° C. @ 31° C. 25° C. 31° C.34° C. SS 605 Toluene 52.10 304.70 220.38 188.56 Methanol 25.37 115.2786.02 59.47 MeCl 20.11 56.63 40.40 31.67 MEK 30.66 204.05 143.31 105.07CPS without carbon black controls Toluene 101.95 15.02 187.60 100.1889.27 Methanol 77.24 16.52 154.72 88.21 75.23 MeCl 32.52 15.23 24.7916.71 14.28 MEK 76.69 16.82 153.72 89.14 71.18 CPS with carbon blackcontrols Toluene 236.64 17.53 183.59 107.84 91.20 Methanol 223.73 15.55135.43 82.18 66.65 MeCl 186.95 15.66 26.72 17.35 14.10 MEK 213.83 16.69146.14 84.29 64.65

All publications, patents and patent applications mentioned in thisapplication are herein incorporated by reference into the specificationin their entirety for all purposes. Although the invention has beendescribed with reference to preferred embodiments and examples thereof,the scope of the present invention is not limited only to thosedescribed embodiments. As will be apparent to persons skilled in theart, modifications and adaptations to the above-described invention canbe made without departing from the spirit and scope of the invention,which is defined and circumscribed by the appended claims.

1. A sensor for detecting an analyte in a fluid, wherein said sensorcomprises a layer comprising conductive modified particles, wherein thelayer comprising conductive modified particles has a preexistingresistance that is altered in the presence of the analyte, wherein saidconductive modified particles comprise carbon products or coloredpigments having at least one organic group covalently bonded to theparticles, wherein said sensor includes an electrical measuringapparatus electrically connected to the layer comprising conductivemodified particles that detects an alteration in the preexistingresistance of the layer in the presence of the analyte.
 2. An array ofsensors for detecting an analyte in a fluid, wherein said arraycomprises two or more sensors for detecting an analyte in a fluid,wherein at least one of the sensors comprises the sensor of claim
 1. 3.The sensor of claim 1, wherein said conductive modified particlescomprise carbon products having at least one organic group attached tothe particles.
 4. The sensor of claim 1, wherein said conductivemodified particles comprise carbon black having at least one organicgroup attached to the particles.
 5. The sensor of claim 1, wherein saidconductive modified particles comprise colored pigments having at leastone organic group attached to the particles.
 6. The sensor of claim 1,wherein said conductive modified particles comprise carbon aerogelshaving attached at least one organic group, pyrolized anion exchangeresins having attached at least one organic group, a pyrolized polymerresin having attached at least one organic group, mesoporous carbonmicrobeads having attached at least one organic group, pelleted carbonpowder having attached at least one organic group, nanotubes havingattached at least one organic group, buckyballs having attached at leastone organic group, densified carbon black having attached at least oneorganic group, carbon clad materials having attached at least oneorganic group, or combinations thereof.
 7. (canceled)
 8. The sensor ofclaim 1, wherein said conductive modified particles comprise anaggregate comprising a carbon phase and a metal-containing speciesphase, wherein said aggregate optionally has attached at least oneorganic group.
 9. The sensor of claim 1, wherein said conductivemodified particles are at least a partially coated carbon black,optionally having attached at least one organic group.
 10. The sensor ofclaim 1, wherein said conductive modified particles are particles havingattached at least one organic group.
 11. The sensor of claim 1, whereinsaid particles are pigments.
 12. The sensor of claim 10, wherein saidorganic group comprises at least one aromatic group, at least oneC₁-C₁₀₀ alkyl group, or mixtures thereof.
 13. The sensor of claim 10,wherein said organic group comprises a polymeric group.
 14. The sensorof claim 10, wherein said organic group further comprises at least oneionic group, ionizable group, or both.
 15. The sensor of claim 10,wherein said organic group comprises a polymer, an alkane, an alkene, analkyne, a diene, an alicyclic hydrocarbon, an arene, a heterocyclic, analcohol, an ether, a ketone, an aldehyde, a carbonyl, a carbanion, apolynuclear aromatic or a derivative of organic, functional group, achiral group, a polyethylene glycol, a surfactant, a detergent, abiomolecule, a polysaccharide, a protein complex, a polypeptide, adendrimeric material, an oligonucleotide, a fluorescent moiety, orradioactive group.
 16. The sensor of claim 10, wherein said organicgroup comprises a 18-carbon alkyl group, a 4-carbon alkyl group, analkyl ester, an oligoether, an anionic group, apoly(chloro-methylstyrene), or a poly(alkylacrylate).
 17. The array ofsensors according to claim 2, wherein each sensor provides a differentresponse for the same analyte with a detector that is operativelyassociated with each sensor.
 18. The array of sensors according to claim2, wherein at least two sensors each comprise a layer comprisingconductive modified particles, wherein the conductive modified particlesfor each sensor are different from each other.
 19. A method fordetecting the presence of an analyte in a fluid, said method comprising:providing a sensor array comprising at least two sensors, wherein atleast one sensor comprises a layer comprising conductive modifiedparticles wherein the layer comprising conductive modified particles hasa preexisting resistance that is altered in the presence of the analyteand wherein the at least one sensor includes an electrical measuringapparatus electrically connected to the layer comprising conductivemodified particles that detects an alteration in the preexistingresistance of the layer in the presence of the analyte; each sensorhaving an electrical path through the sensor; contacting said sensorarray with said analyte to generate a response; and detecting saidresponse with a detector that is operatively associated with eachsensor, and thereby detecting the presence of said analyte, wherein saidconductive modified particles comprise carbon products or coloredpigments having at least one organic group covalently bonded to theparticles.
 20. The method of claim 19, wherein said response is measuredresistance through said electrical path.
 21. The method of claim 19,wherein said method further comprises means to compare the response witha library of responses to match the response in order to determine thepresence of said analyte or the concentration of said analyte.
 22. Anarray of sensors for detecting an analyte in a fluid, said sensor arraycomprising: a first and a second sensor electrically connected to anelectrical measuring apparatus, wherein said first sensor comprises aregion of nonconducting material and a region comprising conductivemodified particles; and an electrical path through said region ofnonconducting material and said region comprising conductive modifiedparticles, wherein the region of nonconducting material and the regioncomprising conductive modified particles have a preexisting resistancethat is altered in the presence of the analyte, wherein said conductivemodified particles comprise carbon products or colored pigments havingat least one organic group covalently bonded to the particles,aggregates comprising a carbon phase and a silicon-containing speciesphase and optionally having attached at least one organic group,aggregates comprising a carbon phase and metal-containing species phaseoptionally having attached at least one organic group, silica-coatedcarbon blacks, or combinations thereof and wherein the electricalmeasuring apparatus detects an alteration in the preexisting resistancein the presence of the analyte.
 23. The array of sensors according toclaim 22, wherein said second sensor is selected from a surface acousticwave (SAW) sensor, a quartz microbalance, an organic semiconducting gassensor, a bulk conducting polymer sensor, a polymeric coating on anoptical fiber sensor, conducting/nonconducting regions sensor conductingfiller in insulating polymer sensors, dye impregnated polymeric coatingon an optical fiber, a polymer composite, a micro-electro-mechanicalsystem device, a micromachined cantilever, or amicro-opto-electromechanical system device.
 24. The array of sensorsaccording to claim 22, wherein said conductive modified particlescomprise carbon products having at least one organic group attached tothe particles.
 25. The array of sensors according to claim 22, whereinconductive modified particles comprise carbon black having at least oneorganic group attached to the particles.
 26. The array of sensorsaccording to claim 22, wherein said conductive modified particlescomprise colored pigments having at least one organic group attached tothe particles.
 27. The array of sensors according to claim 22, whereinsaid conductive modified particles comprise carbon aerogels havingattached at least one organic group, pyrolized anion exchange resinshaving attached at least one organic group, a pyrolized polymer resinhaving attached at least one organic group, mesoporous carbon microbeadshaving attached at least one organic group, pelleted carbon powderhaving attached at least one organic group, nanotubes having attached atleast one organic group, buckyballs having attached at least one organicgroup, densified carbon black having attached at least one organicgroup, carbon clad materials having attached at least one organic group,or combinations thereof.
 28. (canceled)
 29. The array of sensorsaccording to claim 22, wherein said conductive modified particlescomprise an aggregate comprising a carbon phase and a metal-containingspecies phase, wherein said aggregate optionally has attached at leastone organic group.
 30. The array of sensors according to claim 22,wherein said conductive modified particles are at least a partiallycoated carbon black, optionally having attached at least one organicgroup.
 31. The array of sensors according to claim 22, wherein saidconductive modified particles are particles having attached at least oneorganic group.
 32. The array of sensors according to claim 31, whereinsaid particles are pigments.
 33. The array of sensors according to claim31, wherein said organic group comprises at least one aromatic group, atleast one C₁-C₁₀₀ alkyl group, or mixtures thereof.
 34. The array ofsensors according to claim 31, wherein said organic group comprises apolymeric group.
 35. The array of sensors according to claim 31, whereinsaid organic group further comprises at least one ionic group, ionizablegroup, or both.
 36. The array of sensors according to claim 31, whereinsaid organic group comprises a polymer, an alkane, an alkene, an alkyne,a diene, an alicyclic hydrocarbon, an arene, a heterocyclic, an alcohol,an ether, a ketone, an aldehyde, a carbonyl, a carbanion, a polynucleararomatic or a derivative of organic, functional group, a chiral group, apolyethylene glycol, a surfactant, a detergent, a biomolecule, apolysaccharide, a protein complex, a polypeptide, a dendrimericmaterial, an oligonucleotide, a fluorescent moiety, or radioactivegroup.
 37. The array of sensors according to claim 31, wherein saidorganic group comprises a 18-carbon alkyl group, a 4-carbon alkyl group,an alkyl ester, an oligoether, an anionic group, apoly(chloro-methylstyrene), or a poly(alkylacrylate).
 38. A method fordetecting the presence of an analyte in a fluid, said method comprising:providing a sensor array comprising a first and a second sensorelectrically connected to an electrical measuring apparatus, whereinsaid first sensor comprises a region of nonconducting material and aregion comprising conductive modified particles; and an electrical paththrough said region of nonconducting material and said region comprisingconductive modified particles wherein the region of nonconductingmaterial and the region comprising conductive modified particles have apreexisting resistance that is altered in the presence of the analyteand wherein the electrical measuring apparatus detects an alteration inthe preexisting resistance in the presence of the analyte; contactingsaid sensor array with said analyte to generate a response; detectingsaid response with a detector that is operatively associated with eachsensor, and thereby detecting the presence of said analyte, wherein saidconductive modified particles comprise carbon products or coloredpigments having covalently bonded thereto at least one organic group,aggregates comprising a carbon phase and a silicon-containing speciesphase and optionally having attached at least one organic group,aggregates comprising a carbon phase and metal containing species phaseoptionally having attached at least one organic group, silica-coatedcarbon blacks, or combinations thereof.
 39. The method according toclaim 38, wherein said detector is optimized to detect anelectromagnetic energy, optical properties, resistance, capacitance,inductance, impedance, strain, stress, or combinations thereof in saidsecond sensor.
 40. The method according to claim 38, wherein said secondsensor is a surface acoustic wave (SAW) sensor, a quartz microbalance,an organic semiconducting gas sensor, a bulk conducting polymer sensor,a polymeric coating on an optical fiber sensor, aconducting/nonconducting region sensor or conducting filler ininsulating polymer sensor, a dye impregnated polymeric coating onoptical fibers, a polymer composite, a micro-electromechanical systemdevice, a micromachined cantilever, or micro-opto-electro-mechanicalsystem device.
 41. A sensor for detecting an analyte in a fluid, whereinsaid sensor comprises a layer comprising conductive modified particles,wherein said sensor is electrically connected to an electrical measuringapparatus, wherein the layer comprising conductive modified particleshas a preexisting resistance that is altered in the presence of theanalyte, wherein said conductive modified particles comprise carbonproducts or colored pigments having at least one organic groupcovalently bonded to the particles, aggregates comprising a carbon phaseand a silicon-containing species phase and optionally having attached atleast one organic group, aggregates comprising a carbon phase andmetal-containing species optionally having attached at least one organicgroup, silica-containing carbon blacks or combinations thereof.
 42. Asensor for detecting an analyte in a fluid, wherein said sensorcomprises a layer comprising conductive modified particles, wherein thelayer comprising conductive modified particles has a preexistingresistance that is altered in the presence of the analyte, wherein saidconductive modified particles comprise carbon products or coloredpigments having at least one organic group directly attached to theparticles, wherein the sensor includes an electrical measuring apparatuselectrically connected to the layer comprising conductive modifiedparticles that detects a change in the preexisting resistance of thelayer in the presence of the analyte, and wherein the change in thepreexisting resistance is due to a change in the electrical propertiesacross more than one of the conductive modified particles within thelayer.
 43. The sensor according to claim 42, wherein the at least oneorganic group is covalently attached to the particles.
 44. The sensoraccording to claim 42, wherein the at least one organic group directlyattached to the particles is of the chemical form —X-Sp-[A]_(p)-R whereX is attached to the particle and represents an aromatic or alkyl group,Sp is a spacer group, A is an alkylene oxide or polymer and R is aterminal group.
 45. The sensor according to claim 1, wherein the atleast one organic group directly attached to the particles is of thechemical form —X-Sp-[A]_(p)-R where X is attached to the particle andrepresents an aromatic or alkyl group, Sp is a spacer group, A is analkylene oxide or polymer and R is a terminal group.
 46. The sensoraccording to claim 42, wherein each of the conductive modified particlesis an aggregate comprising a carbon phase and a silicon-containingspecies phase having attached at least one organic group.
 47. The sensoraccording to claim 1, wherein conductivity between the conductivemodified particles within the layer changes due primarily toparticle-to-particle distance changes between the conductive modifiedparticles within the layer when the analyte is introduced to the sensor,and wherein the preexisting resistance of the layer changes accordingly.48. The sensor according to claim 1, wherein the organic group isselected from the group consisting of: —C₆H₄—COO⁻X⁺, —C₆H₄—SO₃ ⁻X⁺,—C₆H₄—(PO₃)⁻²2X⁺, —C₆H₂—(COO⁻X⁺)₃, —C₆H₃—(COO⁻X⁺)₂, —(CH₂)_(z)—(COO⁻X⁺),—C₆H₄—(CH₂)_(z)—(COO⁻X⁺), wherein X+ is a caton selected from the groupconsisting of Na⁺, H⁺, K⁺, NH₄ ⁺, Li⁺, Ca₂ ⁺, and Mg⁺, and z is aninteger between 1 and 18 inclusive.
 49. The sensor according to claim42, wherein the organic group is selected from the group consisting of:—C₆H₄—COO⁻X⁺, —C₆H₄—SO₃ ⁻X⁺, —C₆H₄—(PO₃)⁻²2X⁺, —C₆H₂—(COO⁻X⁺)₃,—C₆H₃—(COO⁻X⁺)₂, —(CH₂)_(z)—(COO⁻X⁺), —C₆H₄—(CH₂)_(z)—(COO⁻X⁺), whereinX+ is a caton selected from the group consisting of Na⁺, H⁺, K⁺, NH₄ ⁺,Li⁺, Ca₂ ⁺, and Mg⁺, and z is an integer between 1 and 18 inclusive. 50.A method for detecting the presence of an analyte in a fluid, saidmethod comprising: providing a sensor array comprising at least twosensors, wherein at least one sensor comprises a layer comprisingconductive modified particles wherein the layer comprising conductivemodified particles has a preexisting resistance that is altered in thepresence of the analyte and wherein the at least one sensor includes anelectrical measuring apparatus electrically connected to the layercomprising conductive modified particles that detects an alteration inthe preexisting resistance of the layer in the presence of the analyte;each sensor having an electrical path through the sensor; contactingsaid sensor array with said analyte to generate a response; anddetecting said response with a detector that is operatively associatedwith each sensor, and thereby detecting the presence of said analyte,wherein said conductive modified particles comprise carbon products orcolored pigments having at least one organic group directly attached tothe particles, wherein the change in the preexisting resistance is dueto a change in the electrical properties across more than one of theconductive modified particles within the layer.
 51. The method accordingto claim 50, wherein the at least one organic group is covalentlyattached to the particles.
 52. The method according to claim 50, whereinthe at least one organic group directly attached to the particles is ofthe chemical form —X-Sp-[A]_(p)-R where X is attached to the particleand represents an aromatic or alkyl group, Sp is a spacer group, A is analkylene oxide or polymer and R is a terminal group.
 53. The methodaccording to claim 19, wherein the at least one organic group directlyattached to the particles is of the chemical form —X-Sp-[A]_(p)-R whereX is attached to the particle and represents an aromatic or alkyl group,Sp is a spacer group, A is an alkylene oxide or polymer and R is aterminal group.
 54. The method according to claim 50, wherein each ofthe conductive modified particles is an aggregate comprising a carbonphase and a silicon-containing species phase having attached at leastone organic group.
 55. The method according to claim 19, whereinconductivity between the conductive modified particles within the layerchanges due primarily to particle-to-particle distance changes betweenthe conductive modified particles within the layer when the analyte isintroduced to the sensor, and wherein the preexisting resistance of thelayer changes accordingly.
 56. The method according to claim 19, whereinthe organic group is selected from the group consisting of:—C₆H₄—COO⁻X⁺, —C₆H₄—SO₃ ⁻X⁺, —C₆H₄—(PO₃)⁻²2X⁺, —C₆H₂—(COO⁻X⁺)₃,—C₆H₃—(COO⁻X⁺)₂, —(CH₂)_(z)—(COO⁻X⁺), —C₆H₄—(CH₂)_(z)—(COO⁻X⁺), whereinX+ is a caton selected from the group consisting of Na⁺, H⁺, K⁺, NH₄ ⁺,Li⁺, Ca₂ ⁺, and Mg⁺, and z is an integer between 1 and 18 inclusive. 57.The method according to claim 50, wherein the organic group is selectedfrom the group consisting of: —C₆H₄—COO⁻X⁺, —C₆H₄—SO₃ ⁻X⁺,—C₆H₄—(PO₃)⁻²2X⁺, —C₆H₂—(COO⁻X⁺)₃, —C₆H₃—(COO⁻X⁺)₂, —(CH₂)_(z)—(COO⁻X⁺),—C₆H₄—(CH₂)_(z)—(COO⁻X⁺), wherein X+ is a caton selected from the groupconsisting of Na⁺, H⁺, K⁺, NH₄ ⁺, Li⁺, Ca₂ ⁺, and Mg⁺, and z is aninteger between 1 and 18 inclusive.
 58. The sensor according to claim 1,wherein the alteration in the preexisting resistance of the layer in thepresence of the analyte is a result of swelling of the layer comprisingconductive modified particles.
 59. The method according to claim 19,wherein the alteration in the preexisting resistance of the layer in thepresence of the analyte is a result of swelling of the layer comprisingconductive modified particles.
 60. The array of sensors according toclaim 22, wherein the alteration in the preexisting resistance of thelayer in the presence of the analyte is a result of swelling of thelayer comprising conductive modified particles.
 61. The method accordingto claim 50, wherein the change in the preexisting resistance of thelayer is due to a changed separation distance betweenadjacently-positioned ones of the conductive modified particles withinthe layer, caused by swelling of the layer.